Preheat grill to medium-high. Place patties on grill, turning as required, 7 to 9 min., or until meat is no longer pink and instant-read thermometer reaches 160°F (71°C) when inserted into centre. Top each patty with cheese and allow to melt, about 1 min.
Meanwhile, grill peameal bacon, turning as required, until golden and crisp, about 6 min. Brush with barbecue sauce. At same time, grill onions about 3 min. per side until lightly charred and tender. Top patties with the peameal bacon and grilled onions. Serve on buns brushed with additional BBQ sauce, if desired. Also, garnish with your favourite toppings such as pickles, lettuce and tomatoes.