1.Preheat A Grill For High Heat. 2.Divide The Ground Beef Into Four Portions, And Form Patties Around Pineapple Rings So That None Of The Pineapple Is Showing. In A Small Saucepan, Mix Together The Ketchup, Brown Sugar, And Mustard. Heat Until Sugar Is Dissolved. Set Aside. 3.Place Burgers On The Grill, And Cook For About 5 Minutes Per Side, Or Until Well Done. Spoon Some Of The Brown Sugar Sauce Over The Burgers Before Serving.