Preheat the oven to 450°F and place a rack in the middle position.
In a small bowl, stir together ½ cup grated Parmesan, ½ tsp salt, and ½ tsp garlic powder.
In a large bowl, add 2 lbs broccoli florets and 2 tbsp olive oil; toss until the florets are evenly coated with oil.
Sprinkle the Parmesan mixture over the oiled broccoli and toss again until the broccoli is evenly coated.
Spread the broccoli in a single layer on a large baking sheet, avoiding overcrowding.
Roast at 450°F for 15–18 minutes, until the broccoli is tender and edges are lightly browned (stir or flip once halfway through if you want more even browning).
Remove from the oven and serve immediately.