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 the vegetables are evenly coated.
03 - Slice each chicken breast horizontally through the center without cutting all the way through, then open like a book. Place each butterflied breast 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, tucking in any stray vegetables. Secure with toothpicks to hold the seam closed.
05 - Place the chicken roll-ups seam-side down in the prepared baking dish. Sprinkle any remaining fajita seasoning blend over the tops.
06 - Bake for 25 to 30 minutes, until the internal temperature of the chicken reaches 165°F and the cheese is melted and bubbling.
07 - Remove from the oven and carefully extract the toothpicks. Let rest for 3 to 5 minutes. Garnish with chopped fresh cilantro and serve with lime wedges and sour cream on the side.