Spoon yogurt onto several layers of heavy-duty paper towels; spread to 1/2-inch thickness. Cover with additional paper towels; let stand 5 minutes. Scrape into a food processor or blender using a rubber spatula. Add cheese and next 6 ingredients (through garlic); process until smooth. Transfer yogurt mixture to a bowl; cover and chill 30 minutes.
Sprinkle skinned side of salmon with 1/4 teaspoon salt and 1/4 teaspoon pepper. Place fish, skin side down, on a grill rack coated with cooking spray. Grill 8 minutes or until fish flakes easily when tested with a fork or until desired degree of doneness. Remove and discard skin. Break fish into large flakes with a fork.
Place lettuce in a large bowl. Drizzle with yogurt mixture, tossing to coat. Place 2 cups lettuce mixture on each of 4 large plates; top each serving with 3 ounces salmon.
Wine note: The tang of the yogurt, the "bite" of the garlic, mustard, and Worcestershire, the freshness of the greens, and the succulence of the salmon all mean that the perfect wine for this dish must be clean, crisp, and bracing with enough body to balance a "meaty" fish like salmon. One to try: a California pinot gris like J Pinot Gris from the Russian River Valley, about $15. -Karen MacNeil