For the dumplings, mix the prawns, cabbage, sesame oil, soy, ginger and garlic together in a bowl.
To assemble the dumplings, hold a gyoza wrapper in the palm of your hand and add one teaspoon of the filling mixture. Wet the edges with a little water and seal the dumpling, pinching along the edges to create a fan shape. Repeat the process until all of the filling mixture has been used up (there should be enough for about 30 dumplings).
Heat the oil in a large, lidded frying pan and fry the dumplings for 1-2 minutes, or until crisp. (Do this in batches if necessary.)
Carefully pour in the water. (Caution: the water may spit when added to the hot oil.)
Reduce the heat, cover the pan with a lid and continue to cook the dumplings for 5-6 minutes, or until soft and easy to remove from the pan.
For the dipping sauce, mix the soy sauce, sesame oil and black rice vinegar together in a bowl.
Serve the gyoza dumplings sprinkled with the chopped spring onions and chilli, with the dipping sauce alongside.