Heat 1 tablespoon of oil in a medium non stick frying pan. When it's hot add the mushrooms and fry over a hot heat for 4-5 minutes, until they are golden brown.
Turn the heat down to medium and add the shredded cabbage, spring onions and ginger. Cook until the cabbage begins to change colour and is just tender, around 5-7 minutes.
Stir in the miso paste and cook for one minute (it will soften in the heat and be easier to stir through the cabbage mushroom mixture).
Turn off the heat and add ½ teaspoon of sesame oil. Leave the mixture to cool.
Once cool, make the gyoza.
Take a wrapper and place a teaspoonful of the cabbage mushroom mixture in the middle of the wrapper.
Wet a clean finger in a little water and dampen the edges of the wrapper.
Fold two opposite sides of the wrapper over to meet in the middle and pinch to seal.
Starting on one end, make 3-4 pleats up to the middle, pressing down to seal as you do so. Then do the same from the other end to the middle, pleating to seal. Make sure there are no air pockets.
Place the sealed gyoza on a tray or plate lightly dusted with flour, and repeat with the other 29 gyoza.
You can either place the gyoza in the freezer (to freeze, see notes below), or cook them.
To cook, place ½ tablespoon oil into a large frying pan and place the gyoza into the pan, being careful not to let them touch (you will need to do 2 batches if cooking all the gyoza).
Fry for 2-3 minutes until the bottom of the dumplings are golden brown.
Add 120ml (½ c) water and place a tight fitting lid on the pan. Cook for 3-4 minutes, until most of the water has evaporated.
Take the lid off and let any remaining water evaporate.
Turn the heat off and drizzle a little more sesame oil over the gyoza
Using a spatula, carefully lift the gyoza out and transfer to a plate. If they stick, add a splash more water and wait 15 seconds, then try again.
Eat straight away.