Mix together the mayonnaise and barbecue sauce in a small bowl, then set aside (I did this while I cooked the bacon).
In another bowl, combine the 2 tablespoons of mayonnaise mixture, onion and steak seasoning. Then add the ground beef and mix with your hands. Shape into four patties.
Grill burgers over medium heat for 5-7 minutes on each side or until done, then add cheese and continue to grill for another 1-2 minutes.
Top each burger with grilled bacon, a dollop of mayo mix, and a choice of greens.