Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Wash and scrub the Yukon Gold potato, then cut it into 1/2-inch cubes.
Place the potato cubes on the baking sheet and toss with 1 tsp of olive oil, half of the rosemary, and a pinch of the salt and pepper.
Roast the potatoes for 10 minutes to give them a head start on crisping.
While the potatoes roast, zest the lemon and combine it with the remaining olive oil, rosemary, garlic powder, salt, and pepper in a small bowl.
Rub the lemon-herb mixture over the chicken breast and trim the ends of the green beans.
Remove the baking sheet from the oven, push the potatoes to one side, and place the chicken and green beans on the other side.
Return the sheet to the oven and roast for another 15-20 minutes, or until the chicken reaches an internal temperature of 165°F.
Squeeze the juice from the lemon half over the chicken and vegetables just before serving for a bright, fresh finish.