Spray your casserole dish with cooking spray (I use Pam) and lightly grease with oil.
Mix your spices in a small bowl.
Place your sliced chicken breast in the casserole dish and drizzle with oil. Add salt, pepper and garlic powder to taste.
Next, sprinkle the fajita spice mixture over the chicken (save a little to sprinkle over the veggies). Stir the strips around to coat with the spices.
Top the chicken evenly with the peppers and onion. Sprinkle the remaining spice mixture over the vegetables.
Finally, top the dish off with cheese. I love cheese! Honestly, I didn’t measure out my cheese for this casserole. I tend to cook by eyeballing things. I’m trying to get better about measuring things so I can share the recipe, but when I made this I just added cheese until it looked good!
Bake for 20 minutes, until cheese is melted and casserole is heated through.