Preheat oven to 450° F.
Place cauliflower florets in large roasting pan.
Pull apart onion eights into separate layers then add to the cauliflower.
Stirring occasionally, put black and yellow mustard seeds in a small skillet over medium heat until the yellow seeds darken slightly, about 4-5 minutes.
Remove skillet from heat, add cumin and coriander to skillet and stir constantly (ground spices will burn quickly) for 1 minute. Crush coarsely with mortar and pestle.
Place toasted spices in medium bowl. Whisk in oil, vinegar, curry powder, paprika, and salt. Pour dressing over vegetables; toss to coat. Spread vegetables in single layer.
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.)
Mound vegetables in large bowl.Sprinkle with fresh cilantro. Serve warm or at room temperature.