A burger is not a hamburger when it has cheese on it. It is a cheeseburger. Silly!

Likewise, a burger is not a cheeseburger when it has beetroot, egg, pineapple, lettuce, onion, tomato and other such things on it. It is a kiwiburger. Mmm... kiwiburger... *drools*

So long as my burger doesn't have mushroom, onion, pickles (well, I can stand them, but I'd rather not) and tomato, I'm generally happy with any other standard filling.

EDIT: When I say onion, I don't mind the small bits you get in a McDonalds burger. I mean the massive rings of onion you get on other burgers. Ugh.