Trim the ends of 1 pound of Brussels sprouts and cut them in half lengthwise.
Place the halved sprouts in a large mixing bowl. Drizzle with 3 tablespoons of olive oil, then sprinkle 1 teaspoon garlic powder, 1 teaspoon onion powder, ½ teaspoon salt, and ¼ teaspoon black pepper over the top. Toss well to coat evenly.
Spread the Brussels sprouts cut side down in a single layer on a rimmed baking sheet. Roast at 425°F (220°C) for about 20-25 minutes, flipping halfway through for even crispness.
Remove from oven and immediately sprinkle ½ cup of freshly grated Parmesan cheese over the hot sprouts so it melts slightly. Then zest one lemon over the pan and squeeze the lemon juice evenly on top.
Gently toss to combine cheese and lemon flavors. Serve warm as a flavorful side dish.