I don't know about you but sometimes I really just want a burger. Sure, I could eat the patty without the bun (and I often do) but isn't there something so fun about about picking up a piece of meat sandwiched between two slices of something and just chowing down. Enter: the portabella mushroom cap burger. Ok, so it's not bread, but in my never ending quest to replace complex carbohydrates, it's pretty darn good. Of course for the picky eaters at the table (*cough* husbands & children) you can always replace the mushrooms with a real bun and it'll be probably even more delicious. But it is football season and we are still trying to stick to those New Year's resolution, so for now the bun will suffice.
Now as for the leeks... I love caramelized onions on my burger but they take forever to cook and they also really upset my stomach (tmi?), so the leeks are the perfect alternative. They cook much quicker and serve basically the same purpose. Make sure you salt them well since they do bring a good amount of salt to the dish.
If you hate cilantro as many of you inexplicibly do, you can easily replace the cilantro with parsley, dill, or your favorite herb, or just omit it altogether. It's not crucial to the dish but does bring a nice flavor to the burger.