Preheat oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish.
In a large mixing bowl, combine shredded chicken, black beans, rice, diced tomatoes, corn, 1 cup cheese, sour cream, chili powder, cumin, salt, and pepper. Mix well.
In a small bowl, whisk together the enchilada sauce, 1/4 cup sour cream, and garlic powder.
Layer half of the torn tortilla pieces in the bottom of the prepared dish. Spoon half of the chicken mixture over the tortillas. Drizzle half of the enchilada sauce mixture on top.
Repeat the layers: tortillas, chicken mixture, and remaining sauce.
Sprinkle the remaining 1 cup shredded cheese evenly on top.
Cover with foil and bake for 25 minutes. Then uncover and bake for an additional 10–15 minutes, or until cheese is melted and bubbly.
Let sit for 5 minutes before serving. Garnish as desired.