Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Mince the garlic cloves and finely chop the fresh rosemary leaves.
In a small glass bowl, whisk together the olive oil, lemon juice, lemon zest, minced garlic, and chopped rosemary until well combined.
Place the chicken breast and the trimmed asparagus spears onto the prepared baking sheet in a single layer.
Drizzle the lemon-herb mixture over the chicken and the asparagus, using your hands or a brush to ensure the chicken is fully coated and the asparagus is tossed well.
Evenly sprinkle the sea salt and black pepper over both the chicken and the vegetables.
Roast in the center of the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the asparagus is lightly browned at the tips.
Remove from the oven and let the chicken rest for 5 minutes before slicing to keep it juicy, then serve immediately.