Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Trim the Brussels sprouts and cut them in half; peel the sweet potato and cut it into 1/2-inch cubes.
Place the chicken breast, Brussels sprouts, and sweet potato cubes on the baking sheet.
Drizzle everything with olive oil and sprinkle with garlic powder, sea salt, black pepper, rosemary, and thyme.
Toss the vegetables to coat evenly and rub the seasoning into the chicken breast.
Place the lemon slices on top of the chicken and around the vegetables for extra zest.
Roast in the oven for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are golden brown.
Remove from the oven and let the chicken rest for 5 minutes before slicing to keep it juicy.