Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Cut the Yukon Gold potato into 1/2-inch cubes and trim the ends off the green beans.
Mince the garlic clove and finely chop the fresh rosemary leaves.
In a large bowl, toss the potato cubes and green beans with half of the olive oil, half of the rosemary, sea salt, and black pepper.
Spread the vegetables in a single layer on one side of the prepared baking sheet.
Pat the chicken breast dry and rub with the remaining olive oil, minced garlic, onion powder, and the rest of the rosemary.
Place the chicken on the other side of the baking sheet and roast for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F.
Remove from the oven, drizzle the chicken and vegetables with fresh lemon juice, and let rest for 5 minutes before serving.