Preheat and prep: Heat your oven to 375°F (190°C).
Lightly grease a 9x13-inch baking dish.
Sauté veggies (optional): If using onion and bell pepper, warm oil in a skillet over medium heat. Cook for 5–6 minutes until soft and slightly golden. Season with a pinch of salt and pepper.
Mix the filling: In a large bowl, combine shredded chicken, cooked rice, black beans, corn, half the cheese (about 1 cup), sautéed veggies (if using), taco seasoning, and 1/2 cup of the salsa.
Stir until evenly coated and well mixed.
Layer the base: Spread 1/2 cup enchilada sauce in the bottom of the baking dish to prevent sticking. Add a layer of tortillas, tearing as needed to cover the bottom.
Add the filling: Spoon half the chicken mixture over the tortillas and spread it out. Drizzle with a few tablespoons of enchilada sauce and salsa.
Repeat layers: Add another layer of tortillas, then the remaining chicken mixture.
Top with the remaining enchilada sauce and salsa.
Finish with cheese: Sprinkle the remaining 1 cup of cheese evenly over the top.
Bake: Cover loosely with foil and bake for 15 minutes. Remove foil and bake another 10–12 minutes, until the cheese is melted and bubbly and the casserole is heated through.
Rest and garnish: Let it rest for 5–10 minutes so it sets and slices cleanly. Top with chopped cilantro, green onions, and your favorite fixings.
Serve with lime wedges for a fresh pop.