01 - Preheat oven to 375°F. Lightly grease a 9x13 inch baking dish.
02 - In a skillet over medium heat, cook chopped onion until softened, about 3 minutes. Add 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 enchilada sauce until evenly combined.
04 - Spread ½ cup enchilada sauce on the bottom of the prepared baking dish.
05 - Arrange 5 tortillas over the sauce, tearing as needed to fully cover the base.
06 - Spread half of the chicken mixture over the tortillas and sprinkle with one-third of the shredded cheddar cheese.
07 - Drizzle ½ cup enchilada sauce evenly over the chicken and cheese layer.
08 - Add remaining 5 tortillas, top with remaining chicken mixture, one-third of the cheese, and ½ cup enchilada sauce.
09 - Sprinkle remaining cheddar cheese on top and pour any remaining enchilada sauce over the layers.
10 - Cover with foil and bake for 20 minutes. Remove foil and bake an additional 10-15 minutes until cheese is bubbling and golden.
11 - Allow casserole to rest for 10 minutes before serving. Garnish with chopped cilantro and jalapeño slices if desired. Serve with sour cream.