01 - Preheat oven to 375°F. Lightly grease a 9x13-inch baking dish.
02 - In a skillet over medium heat, sauté chopped onion until softened, about 3 minutes. Stir in cumin, chili powder, garlic powder, and salt; cook for 1 additional minute. Remove from heat.
03 - In a large bowl, mix shredded chicken, black beans, corn, sautéed onions, and ½ cup of enchilada sauce until evenly combined.
04 - Spread ½ cup of enchilada sauce evenly over the bottom of the prepared baking dish.
05 - Arrange 5 tortillas over the sauce, tearing as needed to cover the base completely.
06 - Spread half of the chicken mixture evenly over the tortillas. Sprinkle with one-third of the shredded cheddar cheese.
07 - Drizzle ½ cup of enchilada sauce over the cheese layer.
08 - Repeat layering with remaining tortillas, remaining chicken mixture, another one-third of cheddar cheese, and ½ cup enchilada sauce.
09 - Finish by sprinkling the remaining cheddar cheese and any leftover enchilada sauce over the top.
10 - Cover casserole with aluminum foil and bake in the preheated oven for 20 minutes.
11 - Remove foil and continue baking for 10–15 minutes until cheese is melted, bubbly, and golden brown.
12 - Allow the casserole to rest for 10 minutes before serving. Garnish with chopped cilantro and jalapeño slices if desired. Serve with sour cream on the side.