Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Halve the baby potatoes and trim the tough, woody ends off the asparagus spears.
Place the chicken breast, halved potatoes, and trimmed asparagus onto the prepared baking sheet.
In a small bowl, whisk together the extra virgin olive oil, juice from the half lemon, minced garlic, and finely chopped rosemary.
Drizzle the lemon-herb mixture over the chicken and vegetables, using your hands or tongs to ensure everything is evenly coated.
Sprinkle the sea salt and black pepper over the entire tray.
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 potatoes are golden and fork-tender.
Let the chicken rest for 5 minutes before slicing to keep it juicy, then serve immediately with the roasted vegetables.