Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel the carrots and parsnips, then chop them into one-inch chunks, and halve the Brussels sprouts to ensure even roasting.
Mince the garlic cloves and finely chop the fresh rosemary and thyme leaves, discarding the woody stems.
In a large mixing bowl, toss the prepared carrots, parsnips, and Brussels sprouts with 0.5 tablespoons of olive oil, half of the minced garlic, half of the herbs, and half of the salt and pepper.
Pat the chicken breast dry with a paper towel and rub it thoroughly with the remaining 0.25 tablespoons of olive oil, garlic, herbs, salt, and pepper.
Spread the seasoned vegetables in a single layer on the baking sheet, making a small space in the center to place the chicken breast.
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 and golden.
Remove from the oven and let the chicken rest for 5 minutes to lock in the juices before slicing it and serving with the roasted vegetables.