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 with the spice mixture.
03 - Slice each chicken breast horizontally through the center without cutting all the way through, creating a butterflied piece. Place each butterflied breast between sheets of plastic wrap and use a meat mallet or rolling pin to pound to an even 1/4-inch thickness.
04 - Divide the seasoned vegetable mixture and shredded Monterey Jack cheese evenly among the four pounded chicken cutlets. Lay the filling in the center of each piece.
05 - Roll each chicken breast tightly around the filling, starting from one end and tucking in the sides. Secure each roll with toothpicks to hold the filling inside during baking.
06 - Place the chicken roll-ups seam-side down in the prepared baking dish. Sprinkle any remaining fajita seasoning blend over the tops of the roll-ups.
07 - Bake 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.
08 - Remove from the oven and carefully remove the toothpicks from each roll-up. Let rest for 3 to 5 minutes before serving. Garnish with chopped fresh cilantro and serve with lime wedges and sour cream on the side if desired.