In a small bowl, mix together yogurt, cheese, olive oil, lemon juice, mustard, garlic, Worcestershire, salt and pepper. Set aside.
Cut each head of lettuce in half lengthwise. On the cut side of each romaine half, brush with 1/2 with 1 Tbsp. prepared dressing. Place cut side down on a preheated grill, and grill for 2-3 minutes or until marked.
Place one half head of Romaine, cit side up on each salad plate, and drizzle each with 2 tablespoons dressing. Serve with additional cheese and croutons if desired.
To learn more about your CA privacy rights, please visit CA Privacy Rights