Toss cauliflower florets on a large rimmed baking sheet with onion, thyme, garlic, and oil; season with salt and pepper.
Roast, tossing occasionally, until almost tender, 35-40 minutes.
Sprinkle with Parmesan, toss to combine, and roast until cauliflower is tender, 10–12 minutes longer.
I absolutely love cauliflower. There are so many new recipes for cauliflower out there now that I could eat it 7 days a week. This rather delicious variation comes from Bon Appetit and is a definite keeper in the recipe list.