Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Trim and halve the Brussels sprouts, slice the carrots into half-inch rounds, and roughly chop the red onion.
Toss the vegetables on the prepared sheet with 0.5 tbsp of olive oil and half of the salt and pepper.
Roast for 20-25 minutes, tossing halfway through, until the vegetables are tender and the edges are beautifully caramelized.
Season the chicken breast on both sides with the dried thyme and the remaining salt and pepper.
Heat the remaining 0.5 tbsp of olive oil in a heavy-bottomed skillet over medium-high heat.
Sear the chicken for 5-7 minutes per side until golden brown and the internal temperature reaches 165°F.
Reduce heat to low, add the minced garlic and lemon juice to the pan, and spoon the pan juices over the chicken for 1 minute.
Serve the juicy chicken breast alongside the roasted vegetables for a clean, nutrient-dense meal.