Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Peel the carrots and parsnips, then chop them along with the red onion into uniform 1-inch chunks.
Finely mince the garlic cloves and roughly chop the fresh rosemary and thyme leaves.
In a large mixing bowl, toss the chopped vegetables with 1 teaspoon of olive oil, half of the minced garlic, half of the fresh herbs, and a pinch of salt and pepper.
Place the chicken breast on the prepared baking sheet and rub with the remaining 1 teaspoon of olive oil, garlic, herbs, salt, and pepper.
Spread the seasoned root vegetables in a single layer around the chicken breast on the baking sheet.
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 brown.
Remove from the oven and allow the chicken to rest for 5 minutes before slicing to ensure it remains juicy.
Plate the sliced chicken alongside the roasted vegetables and serve immediately.