Spread enchilada sauce in the bottom of a baking dish.
Add a layer of tortillas, cooked shredded chicken, cheese, and sauce. Repeat the layers, finishing with sauce and cheese on top.
Bake uncovered for about 30 minutes, until heated through and the topping is melted.
Rest for about 15 minutes, then add your preferred toppings and serve.
Notes
Use precooked chicken. Leftovers or rotisserie chicken both work; check store-bought labels if you need to avoid gluten. Use dairy-free shredded cheese and toppings to make the casserole dairy-free. For firmer tortilla layers, briefly toast the tortillas in a dry skillet before assembling. Cover and refrigerate an assembled casserole for up to two days before baking. Store cooked leftovers in an airtight container in the refrigerator for up to four days.