Preheat the oven: Preheat your oven to 400°F (200°C) to ensure the Brussels sprouts crisp up perfectly.
Prep the Brussels sprouts: Trim the ends of the Brussels sprouts, remove any yellow or damaged leaves, and slice them in half.
Prepare the Parmesan mixture: In a large bowl, combine the grated Parmesan cheese, olive oil, garlic powder, onion powder, smoked paprika, salt, and pepper. Stir well to form a paste-like consistency.
Coat the Brussels sprouts: Add the halved Brussels sprouts to the bowl with the Parmesan mixture. Toss them until evenly coated.
Roast the Brussels sprouts: Arrange the coated Brussels sprouts in a single layer on a baking sheet. Roast in the preheated oven for 20-25 minutes, tossing halfway through, until they are golden brown and crispy on the edges.
Finish and serve: Remove from the oven and drizzle with lemon juice (if using) and garnish with chopped parsley for an added burst of flavor.