To make the soy sauce braised shiitake mushrooms: rinse 6 large dried mushrooms under warm water to remove the dust. Combine the mushrooms (without soaking them in water), 1 cup of water, and 1½ tablespoons soy sauce (gluten-free if desired). Bring the liquid to a boil and then reduce the heat to let the mushroom cook in gently boiling water for 20 minutes with the cover on. Remove the cover to let the liquid evaporate so the flavor will be more concentrated. Slice the cooked shiitake mushrooms and serve with the burgers.