Put the meat into a bowl with the garlic, ginger, soy sauce, sake, sesame oil, sugar, potato starch, salt and pepper. In a circular motion (with your hands!) mix the meat quickly until it becomes very smooth and gooey in texture. Add cabbage, onion, and green onions, mix again until everything is combined. Cover bowl with plastic-wrap and let it sit in the fridge for about an hour. Fill Gyouza skins and wrap as desired (there are many ways you can do this, of course) and place the Gyouza in a heated, lightly oiled saute pan. Add hot water into the pan, just enough to cover the Gyouza about half way. Put the lid on and let them cook about med-high until all the water has evaporated. You can add a bit more sesame oil to the pain at this point if you like. Cook Gyouza until the bottoms are golden. That's it! Enjoy!