Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Peel the sweet potato and cut into 1/2-inch cubes, and trim the woody ends off the asparagus.
Mince the garlic and finely chop the fresh rosemary leaves.
Pat the chicken breast dry with a paper towel and rub with half of the olive oil, minced garlic, rosemary, sea salt, and black pepper.
In a small bowl, toss the cubed sweet potatoes with the remaining olive oil and a pinch of salt and pepper.
Place the chicken and sweet potatoes on the prepared sheet pan and roast for 15 minutes.
Remove the pan from the oven, add the asparagus and thin slices of lemon, then return to the oven for another 10 to 12 minutes until the chicken reaches an internal temperature of 165°F.
Let the chicken rest for 5 minutes before slicing to ensure it stays juicy and tender.