1. Dice mozzarella into 1/2-inch (or slightly smaller) cubes. In a large bowl, combine turkey, cheese, Worcestershire sauce, mustard, green onions and egg. Season with black pepper. Form into 4 burgers.
2. Heat a gas or charcoal grill to medium hot. Grill burgers until cooked through, 8-10 minutes, flipping once.
3. Briefly warm bun halves on grill. Spread the bottom of each bun with 1 tbsp mayonnaise. Top with 1 lettuce leave, 1 large slice tomato, turkey burger and top bun.
Per serving: 548 calories, 30g fat, 9g saturated fat, 160mg cholesterol, 725mg sodium, 33g carbohydrate, 4g fiber, 7g sugar, 39g protein