The beef and cheese and ketchup are essential. Bacon optional. Lettuce and tomato totally unnecessary. People probably think they make the burger look better.
As some of the commenters suggest, you could play around with the ingredients. I think I'd do as one of them suggests, and add onion. I'd make them in an oven-proof skillet, and probably also add a little cream at the end. I'm a sucker for sauces.