Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Peel and chop the carrots and parsnips into 1-inch chunks, and trim and halve the Brussels sprouts.
In a mixing bowl, toss the prepared vegetables with 0.5 tablespoons of olive oil and half of the sea salt and black pepper.
Spread the vegetables in a single layer on the baking sheet and roast for 10 minutes.
While the vegetables are roasting, whisk together the remaining olive oil, lemon juice, lemon zest, minced garlic, thyme, and rosemary in a small bowl.
Season the chicken breast with the remaining salt and pepper, then coat it thoroughly with the lemon-herb mixture.
Remove the baking sheet from the oven, move the vegetables to the sides, and place the chicken breast in the center.
Return the pan to the oven and bake for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and caramelized.