Cook the noodles. Bring a large pot of salted water to a boil over high heat. Cook the Ziti according to package instructions until not quite al dente (aka, undercooked). Drain and rinse under cool water to stop cooking. Set aside.
Cook the sausage. Heat olive oil in a large pot over high heat. Add the Italian sausage and cook, breaking apart with a spatula or wooden spoon, until browned and cooked through. Remove sausage to a clean plate and set aside.
Sauté the vegetables. Add 1 tablespoon olive oil to the the same pot over medium high heat. Add the onions and cook, stirring often, until soft and translucent. Add the bell pepper, Italian seasoning, salt, and pepper, and mix well to combine. Reduce heat to medium and continue to cook until green bell peppers have softened, approximately 5 minutes more. Stir in the sliced mushrooms and minced garlic, mixing well to combine. Cook, stirring often, until the mushrooms are cooked and start to release water. Add the crushed tomatoes and mix just to combine.
Blend. Transfer the vegetable mixture to the bowl of a food processor or blender and pulse/blend until desired consistency is reached. I didn’t want a completely smooth sauce, but I also wanted to be sneaky with the vegetables in the hope that my son would eat it (he did!) Go with what works for you and your family.
Mix the sauce and sausage together. Transfer the cooked sausage, blended sauce, and marinara sauce back to the pot over medium heat and mix well to combine.
Preheat oven to 375 degrees F. and spray a large casserole or baking dish with non-stick cooking spray. Set aside.
Prepare the Mozzarella and Ricotta mixture. In a medium bowl mix together half of the shredded mozzarella cheese, ricotta cheese, Mascarpone cheese, and shredded Parmesan cheese.
Layer. Grab your prepared baking dish. Add a thin layer of the sausage and tomato sauce followed by half of the cooked and drained Ziti. Directly on top of the noodles, top with half of the cheese mixture, using your hands or a spoon, if needed, to spread evenly over the top of the noodles. Top with half of the remaining sausage and tomato sauce, followed by the remaining noodles. Finally, top the noodles with the remaining sausage and tomato sauce followed by the ricotta cheese mixture and shredded mozzarella cheese.
Bake. Transfer to the oven and bake until hot, bubbly, and cheese is golden approximately 25 minutes.
Serve. Remove from the oven and sprinkle with fresh chopped Parmesan cheese, if desired. Enjoy!