Preheat your oven to 400°F and line a large rimmed sheet pan with parchment paper for easy cleanup.
Pat the chicken breasts completely dry with paper towels and place them on one side of the prepared sheet pan.
Trim the woody ends off the asparagus and arrange the spears in a single layer on the other side of the pan.
In a small glass jar or bowl, whisk together the olive oil, fresh lemon juice, minced garlic, dried oregano, sea salt, and black pepper.
Drizzle the herb marinade over both the chicken and the asparagus, using your hands or a brush to ensure every piece is well coated.
Thinly slice the half lemon and tuck the rounds around the chicken and over the asparagus for extra aromatic flavor.
Slide the pan into the center of the oven and roast for 20 to 22 minutes, or until the chicken reaches an internal temperature of 165°F.
Remove from the oven and let the chicken rest for 5 minutes before serving to keep the meat juicy and tender.