Chop cabbage finely. Sprinkle 1/4 tsp salt over cabbage and mix. Let sit for 5 minutes, and squeeze out water very well. Do the same for the onion. Cut Nira, Shiitake, and bamboo shoot into very small pieces. Grate garlic and ginger.

In a large bowl, put in all the ingredients (except skins and frying oil), and mix well.

Take a sheet of gyoza wrapper in your hand and place about a tablespoon of the mixture in the center of the wrapper. Moisten the edge along the lower half of the wrapper and fold the upper half of the wrapper up to meet the moistened edge. Fold one of the edges in a series of pleats (about 6), leaving the other edge smooth. Press the edges together to seal the gyoza. Repeat for the rest of the wrappers.

Heat deep-frying oil at medium high heat. Deep fry Gyoza until golden.

Mix soy sauce, rice vinegar, and Rayu chili oil (optional) together for a dipping sauce.