Preheat your oven to 400°F and line a large sheet pan with parchment paper for easy cleanup.
Scrub the sweet potato and cut it into 1-inch cubes, then break the broccoli into bite-sized florets.
Mince the garlic cloves finely and place them in a small bowl with the olive oil, rosemary, thyme, salt, and pepper.
Place the chicken breast, sweet potato cubes, and broccoli florets on the prepared pan.
Drizzle the herb and garlic oil over everything, using your hands or a brush to ensure the chicken and vegetables are evenly coated.
Arrange the ingredients in a single layer, making sure not to overcrowd the pan so the vegetables roast rather than steam.
Roast 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 and squeeze the fresh lemon juice over the entire tray to brighten the flavors before serving.