In a bowl, combine the bread crumbs, onion salt and brown sugar. Add egg. Crumble beef over mixture and mix well. Shape into four patties. Place in a shallow dish; pour barbecue sauce over patties. Cover and refrigerate for 2-4 hours.
In a small bowl, combine the sauce ingredients; cover and refrigerate until serving. For topping, melt the butter in a large skillet. Stir in honey until blended. Add onions; saute for 15-20 minutes or until tender and lightly browned. Keep warm.
Drain and discard barbecue sauce. Grill patties, uncovered, over medium-hot heat for 5-7 minutes on each side or until juices run clear. Top each with a cheese slice; grill 1 minute longer or until cheese is melted. Serve on buns with sauce and onion topping. Yield: 4 servings.