Preheat your oven to 350°F (175°C).
In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the diced chicken, season with salt and pepper, and cook for 5-7 minutes until browned and cooked through. Add the sliced onion, bell pepper, and minced garlic, and sauté for an additional 5 minutes until tender.
In a large mixing bowl, combine the cooked rice with the chicken and vegetable mixture. Stir in the fajita seasoning mix, black beans, diced tomatoes with green chilies, and corn. Mix everything well.
Transfer the mixture to a greased 9x13-inch baking dish. Spread it out evenly, and sprinkle 1 cup of shredded cheddar cheese on top. Cover with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes until the cheese is melted and bubbly.
Let the casserole cool for a few minutes before serving.