Cook the chicken breasts with the seasoning, with the sliced onions and peppers. Cook until chicken is cooked through and peppers and onions are softened.
Lay out 6 tortillas on baking sheets, add a pinchful of cheese to each tortillas. Spoon the chicken fajita ingredients evenly over each of the tortillas. Add another pinchful of cheese over the chicken fajita mixture. Top with the other 6 tortillas.
Bake or grill the quesadillas. Bake at 350 for 10 minutes, flip and bake another 10 minutes. If grilling, grill over indirect heat for 8 to 10 minutes per side, or until tortilla begins to brown. Flip and grill the other side for a few more minutes.
Cut with pizza cutter into 4 or 6 slices each.
Prepare rice and beans or other side dish and garnish.
Serve Chicken Fajita Quesadillas with Rice and Beans.