Fry the shredded cabbage, grated carrots, chopped spring onions and grated ginger in 1 tablespoon of oil over a medium heat until soft and all the water that the vegetables released whilst cooking has evaporated, around 4-5 minutes.
Whisk the soy sauce, miso paste and sesame oil together.
Pour this over the cooked vegetables and add the water chestnuts and cook for 2-3 minutes, stirring, until the liquid evaporates.
Leave to cool.
When cold, mix the chopped chives in to the vegetables.
Lightly dust a plate or baking sheet with flour.
Place a teaspoon of mixture in the centre of each gyoza wrapper, dip a clean finger into some water and use to paint the edges of each wrapper.
Bring the edges together to form a moon shape and pleat to seal (for detailed photos on how to do this, please see in the post above.)
After sealing a gyoza, place it on a floured tray, flat side down (the pleat should be at the top), repeat with the rest of the dumplings.
If freezing, cover and freeze.
When ready to cook the dumplings, heat a non stick frying pan over a medium to high heat and add one tablespoon of oil.
Add the gyoza, flour side down, being careful not to overcrowd the pan - (the dumplings shouldn't be touching). You can cook them in two pans, or cook them in batches.
Once golden, add 120ml (½c) boiling water from a kettle and cover with a well-fitting pan lid or a sheet of tin foil.
Simmer for 4-5 minutes until they have absorbed all the water and are cooked.
Turn the heat off, drizzle over a little sesame oil and using a spatula, carefully lift the dumplings out to a serving plate.
Sprinkle with optional sesame seeds and finely chopped chives.
Eat straight away.
For dipping sauce to serve with the veggie gyoza, please see 2 recipes in the notes.