Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Peel the carrots and parsnips, then chop them along with the red onion into uniform 1-inch chunks.
Mince the garlic cloves and finely chop the fresh rosemary and thyme leaves.
In a mixing bowl, toss the chopped vegetables with half of the olive oil, half of the minced herbs, salt, and pepper.
Place the chicken breast on the prepared baking sheet and rub thoroughly with the remaining olive oil, garlic, and herbs.
Arrange the seasoned vegetables in a single layer around the chicken breast on the baking sheet.
Roast for 25 to 30 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and lightly caramelized.
Remove from the oven and let the chicken rest for 5 minutes before slicing and serving alongside the roasted root vegetables.