I always add a bit of all seasoning, along with garlic, and soy, sometimes bar-b-que sauce, and worcestershire. I don't do fillers in my patties. I don't add onion either, because I think the onion should be sliced on top of the patty. One thing I always do, is when I prepare the meat, because I don't know if it will need anything added, I do a small patty first, and taste it. Obviously you won't, is there a meat eater in the house? Anyway, that helps me to get it right. Then I can just add whatever I think is missing, and they always turn out yummy.