While I resisted the idea of a bunless burger at first, it didn't take me long to realize that was the way to go. Turns out the bun is just a limitation! It keeps you from being able to put on large quantities of toppings, or a variety of sauces that just get soaked up into the bread.
Without the bun, you are only limited by your imagination. This particular burger had lettuce, spinach, onion, pickles, avocado, ketchup, mustard, worcestershire sauce, and two kinds of cheese (and an egg, but it didn't look as pretty).