Heat oven to 400° F. In a small bowl, combine the enchilada sauce and cream. Spoon ¼ cup of the mixture into a shallow 2-quart casserole.
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 for 5 minutes more.
Slice into wedges and serve with the salsa, avocado, and cilantro.