Preheat the oven to 375°F (190°C).
Combine the garlic powder, ground cumin, salt, and black pepper in a small bowl and set the seasoning mixture aside.
In a mixing bowl, stir together the black beans, corn, diced green chiles, diced red bell pepper, and chopped cilantro until evenly mixed.
Place the chicken breasts flat in a large casserole dish and sprinkle both sides with the prepared seasoning mixture.
Spread the corn and bean mixture evenly over the seasoned chicken breasts, then top with the shredded Colby Jack cheese.
Bake uncovered at 375°F for 40–50 minutes, or until the chicken reaches an internal temperature of 160°F; if the cheese browns too quickly, loosely cover with foil for the remaining time.
Let the casserole rest a few minutes after baking, then serve warm.