Preheat your oven to 400°F and line a large sheet pan with parchment paper for easy cleanup.
Slice the chicken breast into 1-inch cubes and peel/chop the carrots and parsnips into similar sizes to ensure even cooking.
In a large mixing bowl, combine the chicken, carrots, parsnips, and halved Brussels sprouts.
Add the olive oil, minced garlic, rosemary, thyme, sea salt, and black pepper to the bowl and toss thoroughly to coat every piece.
Spread the mixture in a single layer on the prepared baking sheet, making sure not to overcrowd the pan so the vegetables can roast rather than steam.
Roast for 20 to 25 minutes, tossing the ingredients halfway through, until the chicken is golden and the vegetables are tender.
Serve immediately while the herbs are fragrant and the chicken is juicy.