Preheat the oven to 400°F (200°C). Line a large baking sheet with parchment paper or aluminum foil.
In a large mixing bowl, toss the green beans with the olive oil, garlic powder, salt, and pepper until the beans are evenly coated.
Spread the green beans in a single layer on the baking sheet. Roast the beans for 15 to 20 minutes, or until they are tender and slightly browned.
Remove the baking sheet from the oven and sprinkle the parmesan cheese over the green beans. Return the baking sheet to the oven and roast for an additional 5 to 7 minutes, or until the cheese is melted and bubbly.
Serve the oven-roasted parmesan green beans immediately, garnished with fresh herbs if desired.