In a large bowl, combine the beef, 2 pineapple slices (chopped finely), soy sauce, onions, ginger, garlic and pepper. Divide the beef mixture into 4 equal portions, shaping each into a 1/2-inch-thick patty.
Preheat the grill. Place the burgers on the grill rack; grill 4 minutes on each side or until desired degree of doneness. Grill the remaining 4 slices of pineapple too. Serve on toasted buns with a slice of pineapple. Drizzle one tablespoon of teriyaki glaze on top of each burger. Serve with desired condiments.
*If you use fresh pineapple, make sure that you take the time to drain the pineapple very well. Fresh is much juicier than canned, and you don't want to end up with a mushy mixture for your burgers.
*Alternately, steak sauce in place of teriyaki glaze is good on these burgers.
*Be sure to grill these burgers as soon as they're shaped and ready to go-- placing them in the refrigerator and letting them sit will allow the pineapple to break down the beef and will make them mushy.