Preheat your oven to 400°F and line a large sheet pan with parchment paper.
Cut the chicken breast into uniform 1-inch cubes for even cooking.
Peel and slice the carrots and parsnips into 1-inch rounds, and roughly dice the red onion.
Mince the garlic cloves finely.
In a large mixing bowl, combine the chicken, carrots, parsnips, and onion.
Drizzle with olive oil and add the garlic, rosemary, thyme, salt, and pepper, tossing until everything is thoroughly coated.
Spread the mixture in a single layer on the prepared baking sheet.
Roast for 25 to 30 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and lightly browned.