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 1-inch cubes and chop the red bell pepper into similar sized pieces.
In a large mixing bowl, combine the chicken cubes, broccoli florets, and bell peppers.
Drizzle the olive oil and lemon juice over the mixture, then sprinkle with rosemary, garlic powder, sea salt, and black pepper.
Toss everything thoroughly until the chicken and vegetables are evenly coated with the oil and seasonings.
Spread the mixture in a single layer on the prepared baking sheet, ensuring enough space for even roasting.
Roast in the oven for 20-25 minutes, or until the chicken is cooked through and the vegetables are tender and slightly browned.
Serve the roasted chicken and vegetables over the warm cooked quinoa for a complete, high-protein meal.