Combine all seasonings for fajita seasoning mix and set aside. REMINDER: this will make 1/2 cup. You will ONLY need a very small amount for this recipe!
Melt 1/2 Tablespoon butter in large skillet over medium heat. Add onions and a pinch of salt and cook, tossing occasionally, for 10 minutes until onions are golden. Add red and green bell peppers and cook, tossing occasionally, for 10 minutes. Remove mixture and set aside
Melt remaining butter in skillet over medium heat. Add chicken, turn heat to medium-high and cook, tossing occasionally, for about 7 minutes until chicken is cooked through and no longer pink. Return pepper and onion mixture to skillet, and season with about 1 1/2 teaspoons of fajita seasoning. Taste, and add a little more if necessary.
Spray a grill pan with cooking spray. Turn heat to medium-low. Warm tortillas for about 30 seconds per side. Remove and set aside
Lay tortilla on a flat surface. Add about 1/4 cup of chicken/onion/pepper mixture to the tortilla, and roll the wrap (see below)
Heat grill pan to medium and place tortilla in grill pan, seam-side down. Press down semi-firmly. Grill for about 3 minutes per side, until you get the golden brown grill marks