Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Pat the chicken breast dry with a paper towel and cut it into 1-inch bite-sized cubes to ensure even roasting.
Peel and chop the carrots and parsnips into 1/2-inch thick rounds, and cut the red onion into small wedges.
In a large mixing bowl, combine the chicken, carrots, parsnips, and onion with the olive oil, minced garlic, chopped rosemary, thyme, sea salt, and black pepper.
Toss everything thoroughly until the chicken and vegetables are well-coated in the herb-oil mixture.
Spread the mixture in a single layer on the prepared baking sheet, making sure not to crowd the pan so the vegetables can caramelize properly.
Roast in the center of the oven for 20-25 minutes, tossing halfway through, until the chicken reaches an internal temperature of 165°F and the vegetables are tender.
Remove from the oven and drizzle with fresh lemon juice before serving to brighten the savory flavors.