In a large mixing bowl, combine the cream cheese, sour cream, and mayonnaise. (If the sour cream is not softened, microwave in the bowl in 30 second increments until it is mainly mixable).
Add the chili powder, cumin, paprika, garlic powder, and salt into the cheese mixture. Season to taste as desired, including more heat from either chili powder, cayenne powder, or hot sauce.
Cut the chicken into 1 to 1.5 inch pieces and add to the bowl.
Cut the bell peppers and onions into strips (like you would for fajitas) and then bite sized pieces and add to the bowl.
Add 1 cup of your shredded cheese to the bowl.
Mix all of the ingredients together.
Spray an 8x8 (or larger) baking dish with nonstick spray.
Pour the chicken mixture into the dish and level out.
Top with the remaining 1/2 cup cheese (or more!).
Bake until the chicken is cooked through, approximately 20 minutes.
Serve with your favorite toppings like salsa, pico de gallo, avocado, etc.
You can use a larger baking dish, however note that the thinner layer will likely result in a quicker cooking time and you will need more cheese to cover the top of the casserole.This casserole is pretty saucy, so it is great to be served on top of rice or vegetables. If you prefer a less soupy casserole, either add 1 Tablespoon thickener like flour or cornstarch, another cup of shredded cheese, or omit the sour cream and mayonnaise.