In a large mixing bowl, combine the halved Brussels sprouts, minced garlic, olive oil, red pepper flakes (if using), salt, and pepper. Toss until the Brussels sprouts are evenly coated.
Spread the Brussels sprouts on a baking sheet in a single layer, cut side down.
Roast in the preheated oven for 20-25 minutes, or until they are golden brown and crisp-tender, stirring halfway through for even cooking.
Once done, remove the baking sheet from the oven and immediately sprinkle the grated Parmesan cheese over the hot Brussels sprouts.
Return the baking sheet to the oven for an additional 5 minutes, or until the cheese is melted and slightly golden.
Remove from the oven and allow to cool slightly. Garnish with fresh chopped parsley before serving.