Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the shredded chicken, sour cream, ½ cup of the enchilada sauce, ground cumin, garlic powder, salt, and pepper. Mix well until combined.
In your baking dish, spread a thin layer of the remaining enchilada sauce at the bottom.
Place 2 tortillas side by side on top of the sauce, tearing them if necessary to fit.
Spread half of the chicken mixture over the tortillas, then sprinkle half of the black beans and corn on top, followed by a third of the cheddar and Monterey Jack cheese.
Repeat the layering process: place 2 more tortillas, the remaining chicken mixture, followed by black beans, corn, and another third of the cheese.
Top the casserole with the last 2 tortillas, drizzle the last of the enchilada sauce over the top, and sprinkle the remaining cheese.
Cover the dish with aluminum foil and bake in the oven for 20 minutes.
After 20 minutes, remove the foil and bake for an additional 10 minutes or until the cheese is bubbly and golden.
Remove from the oven and let it cool slightly before slicing. Garnish with fresh cilantro if desired.