Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Peel and cube the sweet potato into half-inch pieces, then toss them on the baking sheet with half of the olive oil, sea salt, and black pepper.
Roast the sweet potatoes for 10 minutes to give them a head start.
While potatoes roast, mince the garlic and finely chop the fresh rosemary, then rub them onto the chicken breast along with the remaining olive oil, salt, and pepper.
Remove the baking sheet from the oven, move the potatoes to one side, and add the chicken breast and trimmed asparagus to the tray.
Return the tray to the oven and roast for an additional 15-20 minutes, or until the chicken reaches an internal temperature of 165°F.
Drizzle the fresh lemon juice over the chicken and vegetables just before serving to brighten the flavors.