Preheat the oven to 400°F and line a large sheet pan with parchment paper.
Add the sliced chicken, bell peppers, and onion to the sheet pan.
Drizzle with olive oil and toss to coat evenly.
Sprinkle chili powder, cumin, smoked paprika, garlic powder, salt, black pepper, and oregano over the mixture.
Toss again until the seasoning is evenly distributed.
Spread everything into an even layer to avoid overcrowding.
Roast for 22–25 minutes, stirring once halfway through, until the chicken is cooked through and the vegetables are tender with lightly charred edges.
Remove from the oven and rest for 5 minutes before serving.