Soak the koya-dofu in water to rehydrate. Put the cabbage into a food processor to chop. Transfer the chopped cabbage into a bowl. Sprinkle with salt (not listed in the ingredients) and leave to sit for 20 minutes. Squeeze out the water from the cabbage.
Pulse the koya-dofu in your food processor, transfer to a separate bowl, and set aside.
Put the green onions, spring onions, king oyster mushroom, and maitake mushrooms into a food processor and chop finely. Grate the ginger.
Combine the ingredients from Steps 1, 2, and 3 with ● seasonings in a bowl and mix well. Wrap the mixture with gyoza pastries and pan fry.
[Tips for frying:] Heat some sesame oil (not listed in the ingredients) and arrange the gyoza in circle. Fry over medium heat for 4 to 5 minutes. Agitate the frying pan occasionally.
After the bottom of the gyoza has browned, drizzle over a slurry of 50-60 ml water and 1 teaspoon ★ plain flour. Cover with a lid and reduce the heat to low. Continue to fry for about 3 minutes.
Uncover the lid and turn the heat to high. Evaporate the water and cook until crispy. The gyoza with crispy bits are done.
This packet of Chinese stock powder is vegetarian, but if you can't find it, simply omit it.