Mix together mayonnaise and barbecue sauce in a small bowl.
In another bowl, combine the crumbled bacon, 2 tablespoons mayonnaise mixture, onion and steak seasoning; add the ground beef and mix well (it worked best when I just used my hands to incorporate all the seasonings). Shape into four patties.
Grill burgers, covered, over medium heat for 5-7 minutes on each side or until done.
Place a slice of cheese on top. Cover and cook 1-2 minutes longer or until cheese is melted.
Spread remaining mayonnaise mixture over buns.
Place cooked hamburger patty on bun and top with a tomato slice, lettuce, pickles, and onion slice.