Prepare your homemade enchilada sauce (allow at least 1 hour) or use store-bought.
Preheat oven and prepare baking dish. Preheat oven to 350 degrees F and spray a 9 x 13-inch baking dish with non-stick cooking spray. Set aside. Cook the chicken. If you haven't already cooked your chicken, bring a large pot of water to a boil over high heat. Add your chicken (breasts, thighs, mix) and return to a boil. Allow chicken to boil, uncovered for 5 minutes, then cover with a lid and remove from heat. Allow the chicken to rest in the boiled water for an additional 20-25 minutes or until cooked through (cooking time will vary between chicken breasts and chicken thighs so use a digital meat thermometer to be safe). Remove chicken from the pot and allow to rest until cool enough to shred with two forks. Set aside.
Quickly fry the tortillas to soften (and prevent cracking). Add one tablespoon oil to a large skillet over medium heat. When hot add one corn tortilla to the center of the skillet. Allow the tortilla to cook for several seconds then flip (with your hands or a spatula), and immediately add your second corn tortilla to the top (creating a two-layer stack). Continue to cook the first tortilla for several more seconds on the other side. This allows the tortillas to share the excess oil and prevents them from becoming too greasy. Remove the bottom tortilla to a clean plate and flip the top tortilla so that its "dry" side is now facing-down on the skillet. Repeat until all the tortillas have been warmed/browned/oiled, adding additional oil (in small amounts) to the skillet as needed. Remove tortillas to paper towels wrapped in foil to stay warm until ready to roll.
Make the filling. Add the shredded chicken, 1 cup enchilada sauce, 1 1/2 cups shredded cheese, 1 tbsp taco seasoning, and 1/2-1 cup sour cream to a large mixing bowl. Mix well to combine.
Roll your tortillas. Add approximately 1/2 to 1 cup of enchilada sauce to the bottom of your prepared baking dish. Spread evenly to cover the bottom. Unwrap your corn tortillas and, one at a time, spread approximately 1/4 cup of the chicken mixture over each. Roll up each tortilla and place it in the baking dish. Repeat until all tortillas have been filled (or your run out of space).
Add more sauce and cheese. Drizzle the top of the enchiladas with additional enchilada sauce and sprinkle with 1-2 cups of shredded Monterey Jack cheese.
Bake. Transfer to the oven and bake for approximately 15-20 minutes, or until cheese is bubbly and melted.
Serve. Serve immediately with all your favorite toppings including avocado, green onions, cilantro, etc. Enjoy!