01 - Preheat oven to 400°F. Lightly grease a baking dish with olive oil or cooking spray.
02 - In a large bowl, toss the sliced bell peppers and red onion with olive oil, chili powder, smoked paprika, cumin, garlic powder, onion powder, salt, and black pepper until 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 - Evenly divide the seasoned vegetable mixture and shredded Monterey Jack cheese among the flattened chicken cutlets. Lay the filling across the center of each piece, then roll each one up tightly. Secure with toothpicks if needed to hold the shape.
05 - Place the roll-ups seam-side down in the prepared baking dish. Sprinkle any remaining fajita seasoning blend over the top.
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 any toothpicks. Let rest for 3 to 5 minutes. Garnish with chopped fresh cilantro and serve alongside lime wedges and sour cream if desired.