Preheat the oven to 425°F and line a baking sheet with parchment paper.

Slice the Brussels sprouts in half. Toss with drizzles of olive oil and pinches of salt and pepper and spread evenly on the baking sheet. Roast for 20 to 30 minutes, or until tender and golden brown around the edges. The exact timing will depend on the size of your sprouts.

If desired, toss the roasted Brussels sprouts with the lemon juice, zest, Parmesan, and thyme leaves. Garnish with parsley and red pepper flakes.