In a small bowl, combine mayonnaise and barbecue sauce. In another bowl, combine the bacon, 2 tablespoons mayonnaise mixture, onion and steak seasoning; crumble beef over mixture and mix well. Shape into four patties.
Grill burgers, covered, over medium heat for 5-7 minutes on each side or until a thermometer reads 160° and juices run clear. Top with cheese. Cover and cook 1-2 minutes longer or until cheese is melted. Spread remaining mayonnaise mixture over cut sides of bun bottoms. Layer with a lettuce, burger and tomato. Replace tops.