Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Peel the carrots and parsnips, then slice them into 1-inch thick rounds or chunks.
Mince the garlic cloves finely.
In a large mixing bowl, combine the chicken breast, carrots, and parsnips.
Drizzle with olive oil and add the minced garlic, dried rosemary, 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 is not crowded by the vegetables.
Roast in 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 slightly browned.
Remove from the oven and let the chicken rest for 5 minutes before slicing to keep it juicy.
Plate the sliced chicken alongside the roasted vegetables and serve warm.