Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into bite-sized pieces and slice the bell pepper, zucchini, and red onion into uniform strips.
Place the chicken and vegetables onto the prepared sheet pan in a single layer.
Drizzle the olive oil over the chicken and vegetables, then sprinkle evenly with chili powder, cumin, garlic powder, sea salt, and black pepper.
Toss everything together with your hands or tongs until the ingredients are thoroughly coated in the oil and spices.
Roast in the oven for 18 to 20 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and slightly charred.
While the chicken roasts, warm your pre-cooked brown rice in a small saucepan or microwave.
Divide the warm rice into a bowl and top it with the roasted chicken and vegetable mixture.
Finish the bowl by adding the sliced avocado, a bright squeeze of fresh lime juice, and a sprinkle of chopped cilantro.