Preheat the oven to 400°F (200°C).
In a large bowl, combine the sliced chicken, bell peppers, and onion.
Drizzle with olive oil and sprinkle with chili powder, cumin, garlic powder, salt, and pepper.
Toss everything together until well coated.
Spread the mixture evenly on a sheet pan.
Bake for 20-25 minutes, or until the chicken is cooked through and vegetables are tender.
Serve warm on tortillas with optional toppings.