Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Cut the chicken breast into even 1-inch pieces to ensure they cook at the same rate as the vegetables.
Peel the carrots and slice them into 1/2-inch thick rounds; slice the celery into similar 1/2-inch pieces.
In a large mixing bowl, whisk together the olive oil, the juice from the half lemon, minced garlic, rosemary, thyme, sea salt, and black pepper.
Add the chicken pieces, carrots, and celery to the bowl and toss thoroughly until every piece is coated in the herb oil.
Spread the mixture in a single layer on the prepared baking sheet, ensuring the pieces are not overcrowded.
Roast for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the carrots are tender-crisp.
Remove from the oven and let rest for 2 minutes before serving to allow the juices to redistribute.