01 - Preheat oven to 400°F. Lightly grease a baking dish with cooking spray or oil.
02 - In a large mixing bowl, toss the sliced bell peppers and red onion with olive oil, chili powder, smoked paprika, ground 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. 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 cheese evenly among the flattened chicken cutlets. Lay the filling across the center of each piece, then roll up tightly. Secure each roll with toothpicks to hold the filling in place.
05 - Place the chicken roll-ups seam-side down in the prepared baking dish. Sprinkle any remaining fajita seasoning 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 the toothpicks from each roll-up. Garnish with chopped fresh cilantro and serve alongside lime wedges and sour cream if desired.