For the filling
Soak the dried mushrooms in warm water to rehydrate them. Wash and roughly chop the spring onions. Peel the ginger and cut into pieces.
Place the spring onions, mushrooms, prawns, egg and ginger in a food processor and mix to a coarse paste. Season with salt and pepper.
For the gyozas
Lay the gyoza wrappers on your work surface and a spoonful of the filling in the centre of each one. Brush the edges of the gyoza with water and then fold the wrapper in half to make a dumpling. Press the edges together to seal firmly.
Place the dumplings in a steamer and cook for 5 to 8 minutes.