Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Trim the Brussels sprouts and halve them, then peel and slice the carrots into half-inch rounds.
Place the vegetables on the baking sheet, drizzle with half of the olive oil, and season with half of the sea salt and black pepper.
Roast the vegetables for 20 to 25 minutes, tossing halfway through, until they are tender and have crispy, caramelized edges.
While the vegetables roast, season the chicken breast evenly on both sides with garlic powder, dried oregano, and the remaining salt and pepper.
Heat the remaining olive oil in a stainless steel or cast-iron skillet over medium-high heat.
Place the chicken in the hot pan and sear for 5 to 7 minutes per side, or until the internal temperature reaches 165°F.
Remove the chicken from the pan and let it rest for three minutes to keep the juices locked in.
Serve the pan-seared chicken alongside the roasted vegetables and finish with a fresh squeeze of lemon juice over everything.