Preheat your oven to 350°F (175°C).
In a large skillet over medium heat, add the sliced bell pepper and onion. Sauté until they are soft, about 5-7 minutes.
In a mixing bowl, combine the shredded chicken, cooked rice, black beans, diced tomatoes with green chilies, corn, and taco seasoning. Stir until well mixed.
Add the sautéed bell pepper and onion to the chicken mixture and combine thoroughly. Add salt and pepper to taste.
Transfer the mixture into a greased baking dish, spreading it evenly.
Top the casserole with shredded cheese.
Bake in the preheated oven for 30 minutes, or until the cheese is melted and bubbly.
Once done, remove the casserole from the oven and allow it to cool for a few minutes. Garnish with fresh cilantro, if desired.
Serve hot and enjoy your Baked Chicken Fajita Casserole!