Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a small bowl, mix together the chili powder, cumin, garlic powder, onion powder, smoked paprika, salt, and pepper.
Pat the chicken breasts dry and rub the spice mixture all over them. Place the chicken on the prepared baking sheet.
In a large bowl, toss the sliced bell peppers and onion with olive oil, salt, and pepper. Spread the vegetables around the chicken on the baking sheet.
Bake for 20-25 minutes, or until the chicken is cooked through (internal temperature of 165°F) and the vegetables are tender.
Remove from the oven and let the chicken rest for 5 minutes before slicing it into strips.
In meal prep containers, divide the cooked brown rice evenly. Top with sliced chicken, roasted vegetables, and a squeeze of lime juice.
Add sliced avocado and garnish with fresh cilantro before serving or storing in the fridge.