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 pieces to ensure even cooking.
Mince the garlic cloves and finely chop the fresh rosemary and thyme leaves.
In a large mixing bowl, combine the chicken breast, chopped vegetables, olive oil, minced garlic, rosemary, thyme, sea salt, and black pepper.
Toss everything thoroughly until the chicken and vegetables are well-coated in the oil and herb mixture.
Spread the mixture onto the prepared baking sheet in a single layer, ensuring the chicken is not covered 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 root vegetables are tender and golden brown.
Remove from the oven and let the chicken rest for 5 minutes before slicing it against the grain.
Plate the sliced chicken alongside the roasted vegetables and serve immediately.