Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Wash the baby potatoes and cut them into halves or quarters so they are uniform in size; trim the woody ends off the asparagus spears.
Place the chicken breast, baby potatoes, and asparagus onto the prepared sheet pan in a single layer.
In a small bowl, whisk together the olive oil, minced garlic, finely chopped rosemary, sea salt, and black pepper.
Drizzle the herb oil mixture over the chicken and vegetables, using your hands or a brush to ensure everything is evenly coated.
Slice the half lemon into thin rounds and place them directly on top of the chicken breast to infuse flavor while roasting.
Roast in the center of the oven for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the potatoes are fork-tender.
Remove from the oven and let the chicken rest for 5 minutes before serving to keep it juicy.