Combine mince, beaten egg, sauce with grated onion, salt and pepper. Blend together and make into 6 hamburger patties. Grill or barbecue patties for 5-6 minutes on each side. When patties are almost cooked, grill pineapple slices (about 2 minutes) on both sides. Layer hamburger, sliced pineapple, sliced tomato and lettuce on toasted buns. For an interesting variation to your hamburger recipe, add two-thirds of a can of crushed pineapple (very well drained) to your mince before shaping into patties. Brush hamburgers with spicy tropical relish while grilling. Top hamburgers with remaining crushed pineapple for last few minutes of cooking. Brush with relish and heat through.