Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Peel and chop the carrots and parsnips into 1-inch chunks, and slice the red onion into thick wedges.
Mince the garlic cloves finely.
In a large mixing bowl, combine the chicken breast, chopped carrots, parsnips, and red onion.
Drizzle the olive oil over the chicken and vegetables, then sprinkle with the minced garlic, rosemary, thyme, sea salt, and black pepper.
Toss everything thoroughly until the chicken and vegetables are evenly coated in the oil and seasonings.
Spread the mixture in a single layer on the prepared baking sheet, ensuring the chicken pieces aren't 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 caramelized.
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.