Preheat your oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish or casserole dish.
2. Cook the Chicken
In a large skillet, heat the olive oil over medium heat. Add the chicken and cook for about 5-6 minutes, until the chicken is browned and mostly cooked through. Stir in the fajita seasoning to coat the chicken evenly.
3. Sauté the Vegetables
Add the sliced onion, bell peppers, and garlic to the skillet with the chicken. Cook for an additional 4-5 minutes, until the vegetables are tender.
4. Assemble the Casserole
In a large mixing bowl, combine the cooked chicken and vegetables with the sour cream, diced tomatoes with green chilies, and cooked rice (if using). Stir until well combined.
5. Layer the Cheese
Transfer the chicken mixture into the prepared baking dish. Sprinkle the top with the cheddar cheese and Monterey Jack cheese.
6. Bake
Bake the casserole in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly.
7. Garnish and Serve
Once out of the oven, garnish the casserole with fresh cilantro. Serve hot with your favorite toppings, such as guacamole, sour cream, or salsa.
