Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Peel the sweet potato and cut it into 1-inch cubes, and break the broccoli into bite-sized florets.
Mince the garlic cloves finely.
In a mixing bowl, toss the sweet potato cubes and broccoli with half of the olive oil, half of the minced garlic, and a pinch of salt and pepper.
Spread the vegetables in a single layer on one side of the prepared baking sheet.
Pat the chicken breast dry with a paper towel and rub it with the remaining olive oil, garlic, rosemary, thyme, salt, and pepper.
Place the seasoned chicken breast on the other side of the baking sheet.
Roast in the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the sweet potatoes are fork-tender.
Remove from the oven, drizzle the lemon juice over the chicken, and let it rest for 5 minutes before slicing and serving.