Depends on my mood… I’ve been known to change it up often. Sometimes just ketchup, other times mustard, sometimes with onions sometimes without. Sometimes with fried onions. Tomatoes, lettuce, pesto, blue cheese, mayo, bacon, mushrooms..etc. Adding things to the actual burger such as onions, mushrooms (sautated of course), blue cheese crumbles, chedder cheese are all delicious as well. I am still waiting to find some combo of food I really detest. 🙂