Heat your oven to 425F and line a baking sheet with parchment paper.
Rinse the Brussels sprouts then cut off their bottom and then in half.
Drizzle your olive oil onto the Brussels sprouts, toss with a pinch of salt and pepper, then spread it evenly on your baking sheet.
Roast for 25-30 minutes, once the sprouts are golden around the edges.
While the Brussels sprouts are in the oven, in a small bowl, whisk together your lemon, Parmesan, thyme, and red chili flakes. Once the Brussels sprouts are done, toss them together.