Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Peel the carrots and parsnips, then cut them into uniform 1-inch chunks to ensure even roasting.
Mince the garlic cloves and finely chop the fresh rosemary leaves.
In a large mixing bowl, combine the chicken breast, carrots, and parsnips.
Drizzle with olive oil and sprinkle with the minced garlic, rosemary, sea salt, and black pepper.
Toss everything thoroughly until the chicken and vegetables are well-coated in the herb oil.
Spread the mixture onto the prepared baking sheet in a single layer, ensuring the chicken pieces are not crowded.
Roast for 25 to 30 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 let the chicken rest for 5 minutes before slicing.
Plate the sliced chicken with the roasted root vegetables and serve immediately.