Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel the carrots, parsnips, and sweet potato, then dice them into uniform 1-inch cubes to ensure even cooking.
Cut the chicken breast into bite-sized pieces, roughly the same size as the vegetable cubes.
In a large mixing bowl, combine the chicken, diced vegetables, and peeled garlic cloves.
Drizzle with olive oil and sprinkle the dried rosemary, thyme, sea salt, and black pepper over the mixture.
Toss everything thoroughly until the chicken and vegetables are evenly coated in oil and herbs.
Spread the mixture in a single layer on the prepared baking sheet, ensuring they aren't overcrowded so they roast rather than steam.
Roast for 25 to 30 minutes, tossing halfway through, until the chicken is cooked through and the vegetables are tender with caramelized edges.