Preheat the oven to 350 degrees F (175 degrees C). Spray a rimmed baking sheet with cooking spray.
Cut potatoes in half if they are golf-ball-sized or larger. Lay potatoes and green beans in a single layer on the prepared baking sheet and spray with cooking spray. Sprinkle salt, garlic powder, pepper, and parsley on top.
Bake in the preheated oven until potatoes are tender, 25 to 30 minutes.
