01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish with olive oil or nonstick spray.
02 - In a large mixing bowl, combine the sliced bell peppers and red onion. Drizzle with olive oil, then add 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, creating a butterfly cut. Open flat and place between sheets of plastic wrap. Using a meat mallet or rolling pin, pound each breast to an even 1/4-inch thickness.
04 - Divide the seasoned vegetable mixture and shredded Monterey Jack cheese evenly among the four flattened chicken cutlets. Lay the filling in a line along the center of each piece. Tightly roll each breast around the filling and secure with toothpicks to hold the seam closed.
05 - Place the 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, or until the internal temperature of the chicken reaches 165°F and the cheese is melted and bubbling.
07 - Remove from the oven and carefully remove toothpicks. Let rest for 3 to 5 minutes. Garnish with chopped fresh cilantro and serve alongside lime wedges and sour cream if desired.