Heat the grill to medium. Split the wholemeal muffin in half, then lightly toast. Top each half with 1 slice ham, 1 pineapple ring, drained of juice, and a small handful grated mature cheddar. Place on a baking tray and grill for 3-4 mins until bubbling and golden. Splash with Worcestershire sauce and serve by itself or with some crisp salad leaves.