Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish with cooking spray or a little oil.
In a large bowl, combine the shredded chicken, black beans, corn, cumin, chili powder, garlic powder, and a pinch of salt and pepper. Stir until well mixed.
Spread ½ cup of enchilada sauce on the bottom of the dish. Arrange a layer of tortilla pieces to cover, overlapping slightly. Top with half of the chicken mixture, then ½ cup of cheese, then another ½ cup of sauce. Repeat layers, finishing with a final layer of tortillas, remaining sauce, and the rest of the cheese.
Cover the dish with foil (tent lightly to avoid sticking) and bake for 20 minutes. Remove foil and bake for another 10-15 minutes until cheese is melted, edges are bubbly, and internal temperature reaches 165°F (74°C).
Let the casserole rest for 5-10 minutes before slicing. Garnish with cilantro and dollops of sour cream. Serve warm.