Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Scrub the potato and cut it into 1/2-inch cubes, then cut the chicken breast into similar bite-sized pieces.
In a large mixing bowl, whisk together the olive oil, lemon juice, minced garlic, chopped rosemary, sea salt, and black pepper.
Toss the potato cubes and chicken pieces in the lemon-herb mixture until every piece is thoroughly coated.
Spread the chicken and potatoes in a single layer on the prepared baking sheet and roast for 15 minutes.
While the chicken and potatoes roast, trim the woody ends off the asparagus spears and toss them in any remaining marinade from the bowl.
Add the asparagus to the baking sheet and roast for an additional 10-12 minutes until the chicken is cooked through and the potatoes are golden and tender.
Remove from the oven and serve immediately, optionally finishing with a final squeeze of fresh lemon juice.