Preheat oven to 450°F. Place cauliflower florets
in large roasting pan. Pull apart onion quarters
into separate layers; add to cauliflower. Stir
coriander seeds and cumin seeds in small skillet
over medium heat until slightly darkened, about 5
minutes. Crush coarsely in mortar with pestle.
Place seeds in medium bowl. Whisk in oil, vinegar,
curry powder, paprika, and salt. Pour dressing
over vegetables; toss to coat. Spread vegetables
in single layer. Sprinkle with pepper.
Roast vegetables until tender, stirring
occasionally, about 35 minutes. (Can be made 2
hours ahead. Let stand at room temperature. Rewarm
in 450°F oven 10 minutes, if desired.)