Heat oven to 400° F.
In a small bowl, combine the enchilada sauce and cream. Spoon 1/4 cup of the sauce mixture into the bottom of a shallow 2-quart casserole or 9-inch springform pan. Top with 1 tortilla and a third each of the cheese, chicken, onion, and zucchini. Repeat twice to form a total of 3 layers. Top with the remaining tortilla, sauce mixture, and cheese. Cover loosely with foil and bake for 20 minutes. Uncover and bake 10 minutes more. Slice into wedges and serve with the salsa, avocado, and cilantro.
Tip: For a vegetarian version of Quesadilla Pie, replace the chicken with 2 cups fresh corn or frozen corn that has been thawed and patted dry.