Throw peppers, onions, and chicken on a sheet pan, season generously, and let the oven do the work. High protein fajitas without standing over the stove.
Preheat your oven to 425°F (220°C) and line a large sheet pan with parchment paper for easy cleanup.
Slice chicken breasts into thin strips, and cut bell peppers and onion into even 1/2-inch strips to ensure uniform cooking.
Combine chicken, peppers, and onion in a large bowl; drizzle with olive oil and toss well. Sprinkle over chili powder, cumin, paprika, garlic powder, salt, and black pepper, mixing until every piece is well coated.
Spread the seasoned mixture in an even, single layer on the prepared sheet pan, making sure not to crowd the pan.
Bake for 20-22 minutes, stirring once halfway through. Broil on HIGH for 2-3 minutes at the end for some caramelized edges without overcooking the chicken.
Meanwhile, wrap tortillas in foil and place in the oven during the last 5 minutes to warm through.
Remove the pan from the oven and serve the chicken and veggies hot, spooned into warm tortillas.