Preheat the oven to 425°F (218°C).
In a large mixing bowl combine the chicken strips, sliced onion, sliced bell peppers, minced garlic, vegetable oil, lime juice, chili powder, paprika, cumin, ground coriander, garlic powder, salt, and black pepper; toss until everything is evenly coated.
Spread the seasoned chicken and vegetables in a single layer on a large baking sheet.
Bake for 20 minutes, stirring once or twice halfway through to promote even cooking.
Switch the oven to broil and broil 2–3 minutes, watching closely, until the vegetable edges are lightly charred.
Remove from the oven, garnish with chopped cilantro if using, and serve on warmed tortillas with avocado and sour cream.