Prepare dressing: Place garlic, lemon juice, yogurt, mustard, Worcestershire sauce and white wine vinegar in a blender or small food processor. Process until smooth. Add half the cheese, and pulse until mixed in. Start with ¼ cup olive oil, and puree until smooth. Add more if necessary to thin out dressing. Season with salt and pepper to taste.
Brush cut lettuce halves and fish or steak on both sides with dressing.
Grill salmon or steak on an outside grill or in a hot skillet on your stovetop to desired internal temperature. During the last 2 minutes of grilling, place the lettuce cut side down on the grill or in another skillet; grill until lightly browned.
Place lettuce on a plate, grilled side up. Garnish with capers, sun-dried tomatoes and red onion. Serve with the meat or fish. Drizzle both with the remaining dressing. Serve with extra lemon.