Preheat oven to 400°F. Spray a baking dish or sheet pan or line with parchment paper. Peel the outer, discolored leaves off the Brussels sprouts, trim the ends, and cut them in half.
Place the sprouts in a bowl, drizzle olive oil on top, and sprinkle with parmesan cheese, garlic powder, salt and pepper. Toss to coat evenly.
Transfer the Brussels sprouts to the prepared baking sheet, and roast in the preheated oven until golden brown, about 20-25 minutes, depending on their size.