Roasted Cauliflower with Onions, Lemon & Shaved Parmesan. Drizzle olive oil and kosher salt, pepper on cauliflower & onion. Roast chunked cauliflower and onion at 400F for approx 20 min and then toss veg to mix. Continue roasting until really browned and caramelized. Sprinkled shaved parmesan on top. Pop back into oven for a couple minutes to melt slightly, then take pan out of the oven. Squeeze fresh lemon juice all over the veggies and serve.