Preheat and prep: Heat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
Sauté aromatics: In a large skillet over medium heat, add olive oil. Cook the onion and bell pepper for 4–5 minutes until softened.
Stir in garlic and cook 30 seconds until fragrant.
Make the sauce mixture: Reduce the heat to low. Add the enchilada sauce, cream of chicken soup, sour cream, taco seasoning, cumin, and chili powder. Stir until smooth and heated through.
Taste and adjust salt and pepper.
Combine the filling: In a large bowl, mix the shredded chicken, cooked rice, black beans, and corn. Pour in about 2/3 of the sauce mixture and 1 cup of shredded cheese. Stir to coat everything evenly.
Layer the casserole: Spread a thin layer of the remaining sauce on the bottom of the baking dish.
Add a layer of tortilla pieces to cover. Spoon half the chicken filling over the tortillas and spread it out. Sprinkle with 1 cup of cheese.
Repeat: Add another layer of tortillas, the remaining filling, and another 1/2 to 1 cup of cheese.
Top with a final layer of tortillas and the rest of the sauce. Finish with the remaining cheese.
Bake: Cover the dish with foil (tent it slightly so it doesn’t stick to the cheese). Bake for 20 minutes.
Remove the foil and bake another 10–15 minutes, until the cheese is melted and bubbling and the edges are golden.
Rest and garnish: Let the casserole rest for 10 minutes so it sets and slices cleanly. Sprinkle with cilantro and add your favorite toppings.
Serve: Cut into squares and serve with lime wedges, sour cream, and salsa on the side.