Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel and chop the carrots, parsnips, and sweet potato into uniform 1-inch cubes to ensure they cook at the same rate.
In a large mixing bowl, combine the chopped vegetables and the chicken breast, then drizzle with olive oil.
Add the minced garlic, dried rosemary, dried thyme, sea salt, and black pepper to the bowl, tossing everything thoroughly to coat.
Spread the chicken and vegetables in a single layer on the baking sheet, making sure not to overcrowd the pan so the vegetables roast rather than steam.
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 golden brown.
Remove from the oven and let the chicken rest for 5 minutes before slicing to ensure it stays juicy, then serve immediately with the roasted vegetables.