Preheat oven to 450°. Arrange the cauliflower florets in a single layer on a rimmed baking sheet. Drizzle the olive oil over the florets, sprinkle with salt and pepper. Toss to coat the cauliflower evenly with the oil and spread the florets out in a single layer.
Roast the cauliflower, stirring 1 or 2 times, until golden brown and crisp-tender, 15 to 20 minutes.
Toss the cauliflower and sprinkle with parmesan. Roast another 7-10 minutes until the cauliflower is tender and the cheese is melted.
Transfer the cauliflower to plates with a spatula. Serve immediately.