Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Wash and halve the baby potatoes, and trim the tough, woody ends off the asparagus spears.
In a small bowl, whisk together the extra virgin olive oil, lemon juice, minced garlic, and finely chopped rosemary.
Place the chicken breast, halved potatoes, and thin slices of the half lemon onto the prepared baking sheet.
Drizzle half of the lemon-herb oil over the chicken and potatoes, then season everything with sea salt and black pepper.
Roast in the oven for 15 minutes, then remove the pan and add the asparagus spears.
Drizzle the remaining herb oil over the asparagus and return the pan to the oven for 10 to 12 minutes.
Ensure the chicken has reached an internal temperature of 165°F and the potatoes are fork-tender.
Let the chicken rest for 5 minutes before slicing to ensure it stays juicy, then serve with the roasted vegetables.