Preheat oven to 425 degrees F.
Cut off the brown ends of the Brussels sprouts, pull off any yellow and dry leaves, and slice Brussels sprouts in half lengthwise.
In a large bowl, toss Brussels sprouts with 3 tablespoons of olive oil, kosher salt, pepper, and garlic powder if using, coat well.
Transfer them to a large baking sheet lightly greased with olive oil or cooking spray. Roast for 35 to 45 minutes, until crisp on the outside and tender on the inside.
Taste and season with more kosher salt if needed.
Serve warm, sprinkled with grated parmesan if desired.
