Preheat and oil pan over medium heat. Season both sides of chicken breasts with salt and pepper. Cook 5 minutes per side until browned and internal temperature reaches 165°. Remove the chicken from the pan and set aside. Add red onion to the pan and drizzle ½ tsp of oil if needed. Cook until tender and slightly charred, 5-7 minutes. Remove from the pan. While onions are cooking, slice cooked chicken breast in ¼ inch strips. Place a tortilla in a pan, spread BBQ sauce on half of each tortilla. Add a layer of Monterey Jack over top of BBQ sauce. Top with cooked chicken and onions. Layer the remainder of cheese on the empty side of the tortilla. Cook for 3 minutes over medium heat, until the cheese begins to melt. Fold cheese side of the tortilla over meat side and cook 3 additional minutes until cheese is completely melted. Flip half way to avoid burning. Cut the tortilla in half and serve with extra BBQ sauce.