Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Prepare the vegetables by halving the Brussels sprouts, slicing the carrots into half-inch rounds, and cutting the red onion into thick wedges.
Place the chicken breast and the prepared vegetables onto the baking sheet in a single layer.
Drizzle the olive oil over the chicken and vegetables, then sprinkle evenly with rosemary, thyme, garlic powder, sea salt, and black pepper.
Toss the ingredients thoroughly with your hands or tongs to ensure every piece is well-coated in oil and seasonings.
Roast in the center of the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are fork-tender.
Remove from the oven and let the chicken rest for 5 minutes before slicing to ensure the juices redistribute.
Serve the sliced chicken alongside the roasted vegetables while warm.