Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel and dice the sweet potato into 1/2-inch cubes, then place them on one side of the prepared baking sheet.
Toss the sweet potato cubes with 0.5 tbsp of olive oil and a small pinch of the sea salt and black pepper.
Roast the sweet potatoes in the oven for 10 minutes to give them a head start on cooking.
While the potatoes roast, finely mince the garlic clove and the fresh rosemary leaves.
In a small bowl, whisk together the remaining 0.5 tbsp of olive oil, lemon juice, lemon zest, minced garlic, and rosemary.
Pat the chicken breast dry with a paper towel and season both sides with the remaining sea salt and black pepper.
Remove the baking sheet from the oven and place the chicken breast and asparagus spears on the empty side of the pan.
Drizzle the lemon-herb oil mixture evenly over the chicken breast and the asparagus spears.
Return the pan to the oven and roast for 15 to 20 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender.