Heat oven to 400°F. Sauté onion in 1 tablespoon of the oil in a large saucepan over medium heat 5 minutes. Add broth; simmer 10 minutes or until onion is tender. Remove from heat; let cool while roasting cauliflower.
Meanwhile, place cauliflower on a rimmed baking sheet. Drizzle remaining 1 tablespoon oil over cauliflower. Combine 2 teaspoons of the cumin, mustard, turmeric and salt; sprinkle over cauliflower. Toss well and spread into a single layer. Roast 20 minutes or until cauliflower is tender.
Add half of the broth mixture and half of the roast cauliflower to blender container. Cover*; blend until smooth. Return to same saucepan. Repeat with remaining broth mixture and roast cauliflower. Heat through over medium-high heat. Sprinkle remaining 1/2 teaspoon ground cumin over tofu; stir into soup and heat through. Ladle into shallow bowls; top with chives, and, if desired, lemon peel.
* Note: take the round feed tube out of the top of the blender so that when blending hot liquid, steam does not build. Hold a thick towel over the top while blending to prevent the hot liquid from spurting out.
Chive flowers may replace the chopped chives.
Culinary Taste Tip
Add the spice turmeric to the cauliflower while it bakes. It adds flavorful depth and helps improve osteoarthritis pain.
Culinary Technique Tip
Do not wash fresh cauliflower prior to storing. Keep in the refrigerator, with stem side down. Store in a perforated plastic or brown bag or loosely wrap to avoid accumulation of moisture which speeds deterioration.