Preheat your oven to 400°F (200°C) and line a large rimmed sheet pan with parchment paper for easy cleanup and even roasting.
Peel and slice the carrots and parsnips into 1/2-inch thick rounds, and cut the red onion into small, uniform wedges.
In a large mixing bowl, toss the prepared vegetables with half of the olive oil, half of the minced garlic, and half of the salt and pepper until well coated.
Place the chicken breast on the prepared sheet pan and rub thoroughly with the remaining olive oil, garlic, rosemary, thyme, salt, and pepper.
Arrange the seasoned vegetables in a single layer around the chicken on the sheet pan, ensuring they are not overcrowded to allow for proper browning.
Roast for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the root vegetables are tender and golden.
Remove from the oven and let the chicken rest for 5 minutes before slicing to ensure the juices redistribute for a moist and flavorful result.