01 - Preheat the oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - Heat olive oil in a large skillet over medium heat. Add the chopped red onion and sauté until softened, about 2 to 3 minutes.
03 - Add shredded chicken, black beans, thawed corn, cumin, chili powder, garlic powder, salt, and black pepper to the skillet. Cook for 2 to 3 minutes until warmed through. Remove from heat.
04 - Spread 0.5 cup of enchilada sauce evenly on the bottom of the prepared baking dish.
05 - Arrange 4 corn tortillas over the sauce, tearing to fit the dish as needed.
06 - Spread half of the chicken mixture over the tortillas. Drizzle with 0.5 cup enchilada sauce and sprinkle 1 cup cheese evenly on top.
07 - Add remaining tortillas, followed by the remaining chicken mixture, 0.5 cup enchilada sauce, and 1 cup cheese.
08 - Pour the remaining 0.5 cup enchilada sauce over the top layer and cover the dish loosely with aluminum foil.
09 - Bake covered for 20 minutes. Remove foil and continue baking for 10 to 15 minutes until the cheese is bubbly and golden brown.
10 - Allow the casserole to rest for 10 minutes before slicing. Garnish with chopped cilantro, sour cream, sliced avocado, and lime wedges as desired.