Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Prepare the vegetables by trimming the ends of the Brussels sprouts and slicing them in half, and peeling the carrots before cutting them into 1-inch thick rounds.
Place the chicken breast, halved Brussels sprouts, and sliced carrots onto the prepared baking sheet in a single layer.
Mince the garlic and finely chop the fresh rosemary and thyme leaves.
Drizzle the avocado oil over the chicken and vegetables, then sprinkle evenly with the minced garlic, chopped herbs, sea salt, and black pepper.
Toss the vegetables with your hands or tongs to ensure they are well-coated in oil and seasoning, and flip the chicken to coat both sides.
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 tender with golden-brown edges.
Remove from the oven and let the chicken rest for 5 minutes before slicing to ensure the juices stay locked in.