01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish with olive oil or cooking spray.
02 - In a large mixing bowl, combine the sliced bell peppers and red onion with olive oil, chili powder, smoked paprika, ground cumin, garlic powder, onion powder, salt, and black pepper. Toss until vegetables are evenly coated.
03 - Slice each chicken breast horizontally without cutting all the way through, then open like a book to create a butterfly cut. Place between sheets of plastic wrap and pound to an even 1/4-inch thickness using a meat mallet or rolling pin.
04 - Divide the seasoned vegetable mixture and shredded Monterey Jack cheese evenly among the flattened chicken cutlets. Lay the filling across the center of each piece, then roll each breast up tightly. Secure the seams with toothpicks to hold their shape.
05 - Place the rolled chicken pieces seam-side down in the prepared baking dish. Sprinkle any remaining fajita seasoning blend over the top for extra flavor.
06 - Bake on the center rack for 25 to 30 minutes, until the chicken is cooked through to an internal temperature of 165°F and the cheese is melted and bubbling.
07 - Remove from the oven and carefully extract the toothpicks. Garnish with chopped fresh cilantro and serve alongside lime wedges and sour cream if desired.