Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Slice the chicken breast into thin strips and thinly slice the bell peppers and red onion.
In a large bowl, combine the chicken, peppers, and onions. Drizzle with olive oil and sprinkle with chili powder, cumin, garlic powder, salt, and pepper. Toss until everything is evenly coated.
Spread the mixture in a single layer on the prepared sheet pan, ensuring the pieces aren't too crowded so they roast rather than steam.
Bake for 18-22 minutes, or until the chicken is cooked through and the vegetables are tender with slightly charred edges.
While the chicken is roasting, warm your pre-cooked brown rice in a small saucepan or microwave.
Assemble the bowl by placing the rice at the bottom and topping it with the roasted chicken and vegetable mixture.
Garnish with sliced avocado, fresh cilantro, and a squeeze of lime juice before serving.