Combine all ingredients in a bowl. Divide into 4 portions. Form into 3/4 inch thick patties. Make a thumb-print depression in the centre of each patty to prevent rounding while grilling.
Grill over medium-high heat on preheated, oiled grill for 5 to 7 minutes per side. Test doneness with a digital instant-read thermometer inserted sideways into the centre of each patty to ensure they are cooked to 160ºF (71ºC).
To assemble: Place bottom bun on plate, slather with Horseradish Mayo, than some Slaw. Place Beef Sirloin patty and cover with Onion Jam. - see recipes to follow: