01 - Preheat oven to 375°F. Lightly grease a 9x13-inch casserole dish with non-stick spray or butter.
02 - Heat a large skillet over medium heat. Sauté the diced onion and bell pepper for 4 to 5 minutes until softened and fragrant. Add the minced garlic and cook for 1 additional minute, stirring constantly to prevent burning.
03 - Transfer the sautéed vegetables to a large mixing bowl. Add the shredded chicken, cooked rice, black beans, corn, ground cumin, chili powder, smoked paprika, salt, and black pepper. Pour in half of the enchilada sauce and half of the sour cream. Fold everything together until evenly incorporated.
04 - Spread half of the filling mixture into the prepared casserole dish in an even layer. Sprinkle with half of the cheddar and Monterey Jack cheeses. Layer the remaining filling on top. Drizzle with the remaining enchilada sauce and sour cream. Finish with the rest of the cheeses spread evenly across the surface.
05 - Cover the dish tightly with aluminum foil and bake for 20 minutes. Remove the foil and continue baking for another 15 minutes until the cheese is melted, bubbly, and lightly golden on top.
06 - Remove from the oven and let the casserole rest for 10 minutes to set. Garnish individual portions with chopped cilantro, sliced jalapeños, diced tomatoes, or a dollop of sour cream as desired.