Preheat oven to 400°F. Spray a baking sheet with cooking spray.
Place the sliced peppers, onions, and sliced chicken on the baking sheet. Sprinkle the fajita seasoning over the chicken, peppers and onions and drizzle the olive oil over the tops as well. Toss so that everything is evenly coated. Spread into an even layer (don’t want chicken overlapping).
Roast in the oven for 25-30 minutes, tossing halfway through baking time. The veggies will be tender and chicken cooked through. Before removing from the oven cut a chicken in half (or use an instant read thermometer to make sure the chicken has reached an internal temp of 165°F).
Remove from the oven. Serve the filling inside warm tortillas, topped with your desired toppings.
You can use olive oil if you'd like. Olive oil doesn't have as high of a smoke point as vegetable oil, but we are only roasting the veggies and meat at 400°F which is safe enough for olive oil usage.