Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Peel the carrots and parsnips, then slice them into one-inch thick rounds; peel and wedge the red onion into similar sizes.
Finely mince the garlic cloves and 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 sprinkle with the minced garlic, chopped herbs, sea salt, and black pepper.
Toss everything thoroughly to ensure the chicken and vegetables are evenly coated in the oil and seasonings.
Spread the ingredients in a single layer on the prepared baking sheet, ensuring the chicken has space around it to roast properly.
Place the tray in the oven and roast for 25 to 30 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are golden and tender.
Remove from the oven and allow the chicken to rest for 5 minutes before slicing it into strips.
Serve the sliced chicken alongside the roasted root vegetables while warm.