Preheat the oven to 425 degrees.
Saute the onion, zucchini and mushrooms in the olive oil until tender.
Puree the tomatoes, peppers, garlic and seasonings together.
Mix the chicken in with the vegetables, along with 1 cup of the sauce mixture.
Place ½ cup of the sauce in the bottom of a 9x13 baking dish. Top with 6 tortillas, ½ of the chicken and ½ the cheese.
Repeat with another layer of tortillas, chicken and cheese. Top with a final layer of tortillas. Bake for 15-20 minutes.
Serve with a garnish of sour cream.