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 into 1-inch rounds; slice the red onion into thick wedges.
Mince the garlic cloves and finely chop the fresh rosemary and thyme leaves.
In a large mixing bowl, combine the chicken breast, carrots, parsnips, and red onion.
Drizzle the olive oil over the mixture and add the minced garlic, rosemary, thyme, sea salt, and black pepper.
Toss everything together until the chicken and vegetables are thoroughly and evenly coated with the oil and herbs.
Spread the ingredients in a single layer on the prepared baking sheet, ensuring the chicken pieces are not crowded by the vegetables.
Roast in the center of the oven for 25 to 30 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 before slicing to keep it juicy.
Plate the chicken alongside the roasted root vegetables and serve immediately.