Preheat oven to 350°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 until emulsified. Pour dressing over vegetables; toss to coat. Spread vegetables in single layer. Sprinkle with pepper.
Roast vegetables until tender, stirring occasionally, about 30 minutes. Add peas and continue roasting until cauliflower is tender, 10-15 additional minutes. Mound vegetables in large bowl. Sprinkle with fresh cilantro. Serve warm or at room temperature.
adapted from Bon Appétit: R.S.V.P., September 2004 (from Epicurious.com)