In a small bowl, whisk together the mustard, soy sauce, garlic, and oregano. Set aside.
In a non-stick skillet, cook the hamburger patty to your liking. Once you flip the hamburger to cook the other side, add both cheeses so that they will melt on top of the patty. Remove patty from the heat to a small plate.
In the same skillet, saute the mushrooms until tender. Remove from the heat.
Lay lettuce leaves flat on your serving plate and add the leeks, tomato, and pickle. Add the hamburger patty with melted cheese, spread the Dijon sauce on top, and top it off with the sauteed mushrooms.
Tuck in both ends of the lettuce and roll it up around the patty and the vegetables.