Soak the zucchini, cabbage, bean sprouts, mushrooms, and onions in a pinch of salt, individually
Mix together all ingredients with 1 egg to bind it all together
Take a spoonful of the veggie mixture and place in the center of the mandu wrapper
With your thumb and index finger, carefully pinch together both sides of the wrapper to create a "pouch" so the mixture will not leak out. It's important to use water on your finger tips to keep them from sticking to the wrapper. Also note that you don't want to overfill the mixture otherwise it's easy for the wrapper to break.
Once you've created all of your mandu "pouches", cook in medium-high heat in an oil of your choice.
Wait until one side is brown, then add in 1 cup of water to the pan and cover the pan so that the other side can cook to completion.