Preheat oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
In a large mixing bowl, combine chicken cubes, broccoli, bell peppers, and red onion.
Drizzle olive oil over the mixture and sprinkle with garlic powder, oregano, paprika, salt, and pepper.
Toss thoroughly until all ingredients are evenly coated with oil and seasoning.
Spread the mixture onto the prepared sheet pan in a single, even layer, ensuring no overcrowding.
Roast in the center rack of the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F (74°C).
Remove from oven and let rest for 5 minutes before serving.