Preheat oven to 400°. Cover a sheet pan with foil or parchment paper
Put green beans in a bowl. Drizzle with enough olive oil to lightly coat all the beans. Season with salt and pepper. Sprinkle with the parmesan cheese and toss well.
Spread the beans in a single layer on the sheet pan. A little space between the beans is a good thing! Roast in the oven for about 20 minutes or until the beans are somewhat shriveled and the parmesan is browning. You'll need to check them. The exact cooking time will vary based on the relative water content of your beans, which is unpredictable.