This delicious Zucchini Casserole is a cheesy, creamy, and comforting side dish made with fresh zucchini and yellow squash, mayonnaise, sour cream, panko breadcrumbs, and lots of cheese. It’s so easy to make and pairs perfectly with all your dinnertime favorites like chicken, beef, or fish.
Cheesy Zucchini Casserole
This cheesy, creamy, comforting zucchini casserole is impossible to resist. One bite and poof, the entire thing is gone—probably inside your belly.
Like cauliflower, zucchini is mild and super versatile, making it the perfect vegetable for casseroles, picky kiddos, or anyone hoping to fill their dinner plates with extra greens.
Made with super simple ingredients like fresh zucchini, mayonnaise, sour cream, and plenty of cheese, this incredible zucchini casserole is guaranteed to please everyone! Serve it as a low-carb side dish with your favorite main dishes, or add it to your holiday meal plan.
Key Ingredients and Substitutions
Find the printable recipe with measurements in the recipe card below.
- Zucchini: It is really hard to give the exact number of zucchini (or zucchini plus yellow squash) you’ll need to make this casserole. At a minimum, you’ll need four medium-sized zucchini. I always make sure to have one extra squash on hand, just in case.
- Butter: To sauté the garlic and onion. Olive oil can also be used.
- Garlic: Freshly minced garlic is added for flavor.
- Onion: Sautéed yellow onion adds extra savory flavor.
- Sour Cream: For creamy, tangy flavor. Full-fat sour cream is recommended.
- Mayonnaise: The mayonnaise mixes with creamy sour cream and melted cheese for a rich and decadent sauce.
- Egg: Helps thicken the sauce.
- Cheese: This recipe calls for freshly grated parmesan, cheddar, and mozzarella cheese.
- Panko Breadcrumbs: For the crispy buttery topping.
Is it Keto?
Not quite. However, you can easily make it keto by skipping the panko breadcrumbs entirely or replacing them with a keto-approved alternative like fried pork panko.
How to Make Zucchini Casserole
1. Preheat the oven and spray a 1.5 quart (1.5L) casserole dish with non-stick cooking spray.
2. Prepare the zucchini: Zucchini is made up of 95% water. To prevent a watery, mushy, soggy casserole, we need to salt and drain the zucchini for at least 30 to 45 minutes before cooking. Slice the zucchini into 1/4-inch rounds, toss in 1-2 teaspoons salt, and place in a colander set inside the sink. After they have drained, transfer the zucchini to a clean kitchen towel lined with paper towels. Gently pat the zucchini dry.
3. Saute the onions: Cook the onions and garlic in butter or olive oil until softened, then set aside to cool.
4. Prepare the creamy cheese mixture: Combine the sour cream, mayonnaise, eggs, grated parmesan cheese, ½ cup of shredded cheddar cheese, and ½ cup of mozzarella cheese in a large bowl. Add the cooled onions and mix well. Additional salt is not needed.
5. Assemble: Arrange the zucchini slices in overlapping rows (see image). Pour the creamy onion and cheese mixture over the top and smooth the surface with a wooden spoon.
6. Bake for 20 minutes, then carefully remove from the oven. Meanwhile, as the casserole is baking, melt the remaining two tablespoons of butter in a small bowl and combine with the panko breadcrumbs.
7. Top with the panko and cheese and continue to bake for an additional 20-25 minutes.
What to Serve with Zucchini Casserole
This zucchini casserole is the perfect side dish for baked salmon or pan-seared steak. It’s also great for holidays and family gatherings. In fact, it’s recently become a must-have addition to our Thanksgiving table.
Storage and Freezing
Transfer leftovers to an airtight container and place in the refrigerator for up to 3-4 days. Reheat in the microwave or in the oven preheated to 350 degrees F until heated through.
Freezing is not recommended, as the texture will change too much after thawing.
More Zucchini Recipes
- Roasted Zucchini with Parmesan
- Zucchini Boats
- How to Make and Cook Zucchini Noodles (Zoodles)
- Baked Zucchini Fries
- Sauteed Zucchini
- Cheesy Zucchini Bread (Quick Bread)
- Healthy Corn and Zucchini Chowder
Tools for this Recipe
Check out all of my kitchen essentials here (Amazon affiliate links*)
- 1.5-quart baking dish
- Colander – a must-have for rinsing vegetables, draining, and straining.
- Skillet – I still own, use, and love the Calphalon cookware set that I purchased more than a decade ago.
- Box Cheese Grater – For shredding the cheese.
- Mixing Bowl – Either stainless steel or glass mixing bowl
- Garlic Press
*As an Amazon Associate, I earn a small percentage from qualifying purchases.
RECIPE CARD
Zucchini Casserole
Ingredients
- 4 medium zucchini squash - (sliced in 1/4" thick slices) see notes
- salt
- 4 tablespoon butter - divided
- 1 yellow onion - finely chopped
- 2 cloves garlic - minced
- ¼ black pepper
- ½ cup sour cream
- ½ cup mayonnaise
- 2 eggs - slightly beaten
- ½ cup grated parmesan cheese
- 1 cup shredded cheddar cheese - divided
- ½ cup shredded mozzarella cheese
- 1 cup panko breadcrumbs
Instructions
- Preheat the oven to 375 degrees Fahrenheit. Spray a 1.5 quart (1.5L) casserole dish with non-stick cooking spray.
- Place the sliced zucchini in a large colander set over the kitchen sink. Toss the zucchini with salt (approximately 1-2 teaspoons). Drain the zucchini for at least 30-45 minutes. This step prevents us from ending up with a watery, soggy casserole. After the zucchini has drained, transfer them to a clean kitchen towel lined with paper towels. Gently pat the zucchini dry. Set aside.
- As the zucchini slices drain, soften the onions. Add two tablespoons of butter to a medium skillet set over medium heat. Add the onions and cook, often stirring to prevent burning, until the onions have softened. At the last minute, add the minced garlic and black pepper. Mix well to combine, then remove from heat. Set aside to cool completely.
- In a large bowl combine the sour cream, mayonnaise, eggs, grated parmesan cheese, ½ cup of shredded cheddar cheese, and ½ cup of mozzarella cheese. Once the onion and garlic mixture has cooled to room temperature, combine with the cheese mixture.
- Transfer the drained zucchini slices to the prepared baking dish. Arrange in several overlapping rows. Additional salt is not needed.
- Pour the creamy onion and cheese mixture directly over the top of the zucchini slices. Use a wooden spoon or spatula to smooth the surface.
- Transfer to the oven and bake for 20 minutes.
- Melt the remaining two tablespoons of butter in a small bowl in the microwave and combine with the panko breadcrumbs.
- Carefully remove the casserole from the oven. Top with the panko breadcrumbs and the remaining half cup of shredded cheddar cheese. Return to the oven to bake for an additional 20-25 minutes, or until the cheese is melted and bubbly and the breadcrumbs are golden brown.
Jessica’s Notes
- It is really hard to give an exact number of zucchini (or zucchini plus yellow squash) that you’ll need to make this casserole. At a minimum, you’ll need 4 medium-sized zucchini. I always make sure to have one extra squash on hand just in case.
- Leftovers: Keep leftovers stored in an airtight container in the refrigerator for up to 4 days. Reheat in the oven preheated to 350 degrees F or in the microwave until heated through.
- I do not recommend freezing.
- To make this recipe gluten-free, you may either omit the breadcrumbs or purchase breadcrumbs that are certified gluten-free.
Nutritional Information
(Nutrition information provided is an estimate and will vary based on cooking methods and specific brands of ingredients used.)
Made this twice now….Wouldn’t change a thing!
I love hearing that, Diane 😀
Good recipe ! Just letting you know that the 1.5 casserole dish you tagged is no longer available on Amazon. You may want to choose another one to keep getting credits for it. I have a 6.5 x 10 in that worked well. I may try a 9×13 next time to have more topping??? Thoughts or adjustment needed??
Thanks GMJ. Using a 9×13 dish for a zucchini casserole originally designed for a 1.5 qt dish will significantly alter the dish’s depth, likely making it thinner and potentially affecting cooking times and texture. You may need to adjust the cooking time downwards to prevent overcooking, and consider increasing the amount of topping to ensure an even layer across the larger surface area. Monitoring the casserole closely during cooking will be key to making these adjustments successfully.
Excellent recipe. Was concerned about the residual salt in zucchini. Did rinse it twice. I did use Italian panko which added a great flavor. Combination of the sauce was very creamy.
I appreciate your excellent feedback, Susan 😀
Hello Jessica Brian, here. I am a man who cannot. eat onions. So, I make recopies and do not add the onion and they are great and taste good. Being in the culinary industry most of my life I enjoy looking and finding dishes that I would enjoy making and eating. and this one here is a good one minus the onion. Thank you for all of the recipes they are all good ones.
Thanks for the feedback, Brian 🙂
Very good added Tofu
Thanks 🙂
This recipe is boss. I did doctor it up such as including sautéed vegan sausage to the zucchini layer and extra spices to the onion and breadcrumb parts, but other than that…. perfecto *thumbs up*. This is a main dish.
I appreciate your boss feedback, Rachaele 😀
I could not find a list of ingredients. How many eggs, how much mayonnaise and soy cream??
The ingredient list is in the Zucchini Casserole Recipe card directly above 🙂
My eggs scrambled. Don’t know what happened.
Without being next to you while you were cooking, its hard to say, but I am guessing that you may have not let the onion/garlic cool before mixing it with the eggs in step 4:
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In a large bowl combine the sour cream, mayonnaise, eggs, grated parmesan cheese, ½ cup of shredded cheddar cheese, and ½ cup of mozzarella cheese. Once the onion and garlic mixture has cooled to room temperature, combine with the cheese mixture.
“
This recipe if absolutely delicious! I would recommend using finely grated parmesan cheese. It tends to clump otherwise.
Thanks for the recommendation and feedback, Carolyn 😀
It’s August in New England, so I riffed on this a little bit… Followed the zucchini part, but also steamed some cauliflower which I added along with adding a layer of sliced tomatoes to the top before going in the oven. This was so good!!! Next time I’ll add more tomato & feel like I could use just about any veggie. This recipe is amazing, surprisingly unique and a total winner!!
Please verify what the size of a medium zucchini is…I used two ‘medium’ zucchinis, and apparently the zukes you have are a different size than our’s here in Minnesota. Since I had only two zukes, I halved the other ingredients and followed the recipe and mine were dry and not at all creamy. My zukes were about 1.5 to 2 inches in diameter. Plz clarify what size zuke is ‘average’ in your recipes. Thx. D.
A medium-sized zucchini is typically about 8-10 inches long and around 2 inches in diameter.
So good! Everyone raved about it and said it needed to be added to the Thanksgiving menu.
This zucchini casserole is definitely a great addition to any Thanksgiving table 🙂
Thanks for the review and rating, Marilyn!
Very tasty. The only thing I added was fresh herbs from my garden. My husband liked it and he doesn’t usually enjoy breadcrumb topped casseroles. We will make again.
I appreciate the tasty feedback and rating 😀
Can it be made the night before baking minus the Pablo of course?
It came out very tasty an flavorful.
Tasted great!