When picking cauliflower at the store, look for orange or purple varieties—they're both rich in antioxidants.
Preheat oven to 450°F. On a baking sheet, drizzle cauliflower with 2 Tbsp. oil; sprinkle with 1/2 tsp. salt and toss to coat. Spread in a single layer. Roast, stirring once or twice, until golden brown and tender but not mushy, about 15 minutes. Taste a floret for doneness; larger florets may take slightly longer to cook.
Make salsa verde: In a small bowl, stir parsley, chives, capers, mustard, lemon zest, pepper and remaining 1/4 tsp. salt until well mixed. Stir in remaining 4 Tbsp. oil and olives. (The salsa verde can be made up to 1 day in advance. Refrigerate, covered, until serving.)
Transfer cauliflower to a platter and drizzle with salsa verde. Serve hot or at room temperature.
Adapted with permission from Brassicas, by Laura B. Russell (Ten Speed Press, copyright 2014).