Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Pat the chicken breast dry with a paper towel to ensure a golden sear, then place it on one side of the baking sheet.
In a small bowl, whisk together the olive oil, lemon juice, lemon zest, minced garlic, oregano, sea salt, and black pepper.
Brush half of the lemon-herb mixture over the chicken breast, ensuring it is evenly coated on all sides.
Trim the woody ends off the asparagus and arrange the spears in a single layer on the other side of the baking sheet.
Drizzle the remaining herb mixture over the asparagus and toss lightly to coat, then top the chicken with the fresh rosemary sprig.
Roast in the oven for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the asparagus is tender.
Let the chicken rest for 5 minutes before slicing to keep it juicy, then serve with a final squeeze of fresh lemon.