Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Prepare the vegetables by trimming and halving the Brussels sprouts, slicing the carrots into thin coins, and roughly chopping the red onion.
Mince the garlic cloves and whisk them together in a small bowl with the extra virgin olive oil, rosemary, thyme, sea salt, and black pepper.
Cut the chicken breast into 1-inch bite-sized cubes to ensure they roast at the same rate as the vegetables.
Place the chicken pieces and all the chopped vegetables onto the prepared baking sheet.
Drizzle the garlic-herb oil over the chicken and vegetables, then use your hands to toss everything thoroughly until evenly coated.
Spread the mixture out into a single layer, ensuring the chicken pieces are not crowded so they can brown properly.
Roast for 20 to 25 minutes, tossing the ingredients halfway through, until the chicken is cooked through and the vegetables are tender and golden.