I had a pretty kickass "greek burger" at a vegetarian restaurant a couple years back, when I went out with a couple herbivore friends of mine.
It was some kind of sourdough brioche something bun, a onion/mushroom patty made in house, herbs, olives, red onions, lettuce, feta, probably a few other things I'm missing, and piles of it so the thing made a mess when you were eating it. And they didn't go easy on the olive oil - I think they realized that a really good burger is also a bit greasy, and put that in. And the fries on the side were really well done, and they had a few different things (not just ketchup) and malt vinegar and other stuff for the fries.
All of the individual parts were good in their own right though. Good bread, mushrooms/onions/garlic are good, I love greek salad... throw all that together in a well executed fashion and it's gonna be good.