Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Trim the Brussels sprouts and halve them, slice the carrot into rounds, and chop the red onion into wedges.
Toss the vegetables with 0.5 tbsp of olive oil, half the sea salt, half the pepper, and half the dried thyme on the prepared baking sheet.
Roast the vegetables for 20-25 minutes until they are tender and have developed a crispy, caramelized exterior.
While the vegetables roast, season the chicken breast with the remaining salt, pepper, garlic powder, and thyme.
Heat the remaining 0.5 tbsp of olive oil in a skillet over medium-high heat.
Sear the chicken for 5-7 minutes per side until the internal temperature reaches 165°F and the outside is beautifully browned.
Let the chicken rest for 5 minutes before slicing and serving alongside the roasted vegetables.