Preheat oven to 425° F. On a large rimmed baking sheet, toss Cauliflower florets, onion, thyme and garlic with 2 tablespoons of olive oil. Roast, tossing occasionally, for 30-40 minutes, until almost tender. While cauliflower roasts, combine grated Parmesan cheese and bread crumbs. When cauliflower is nearly finished, sprinkle the cheesy breadcrumb mixture onto cauliflower and broil until golden brown, about 10 more minutes. Serve immediately.