Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Peel the carrots and parsnips, then chop them into uniform 1-inch chunks to ensure even cooking.
In a small bowl, whisk together the olive oil, minced garlic, finely chopped rosemary, sea salt, and black pepper.
Place the chicken breast and the chopped root vegetables in a large mixing bowl and drizzle with the herb oil mixture.
Toss everything thoroughly until the chicken and vegetables are well-coated in the aromatics.
Spread the mixture onto the prepared baking sheet in a single layer, ensuring the chicken has space around it.
Roast for 20 to 25 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 and serving alongside the roasted vegetables.