Preheat the oven to 400ºF. Prepare a baking sheet: line a baking sheet with parchment paper OR foil sprayed with nonstick cooking spray. You can also spray the baking sheet directly. Set aside.
Prepare the Brussels sprouts: Scrub the Brussels sprouts under warm water to remove any dirt. Pat dry with a towel. Use a sharp knife to cut both ends off of each Brussels sprout. If some of the leaves fall off, don't worry! You'll roast these, too. Then, cut them in half longways (hot-dog style). The goal is to get all of the Brussels sprouts around the same size so that they roast evenly. If you have some extra-large sprouts, you may need to quarter them. Transfer the Brussels sprouts to the prepared baking sheet.
Drizzle the veggies with a generous amount of olive oil salt and season with garlic powder, salt, and pepper. Use your hands to massage the oil and spices into the veggies.
Evenly spread the Brussels sprouts out onto the baking sheet. Make sure they don't touch – if they overlap at all, they will not roast evenly.
Bake for 20-25 minutes, tossing the Brussels sprouts every 10 minutes.
Remove the baking sheet from the oven and sprinkle the grated parmesan cheese on top of the Brussels sprouts.
Bake for another 3-5 minutes or until the Brussels sprouts are golden brown and crispy.