Combine cabbage and ½ tsp salt in a bowl. Set aside for 20 minutes to allow cabbage to release moisture.
Place remaining ingredients (excluding gyoza wrapper) into a large bowl. Squeeze out any excess water from cabbage before adding into the bowl.
Combine well ingredients in the bowl and wrap filling into gyoza wrapper.
Heat 1 tbsp oil in a large skillet over medium heat. Place gyoza in rows and cook until the underside is light golden. Pour 1/3 cup of water around the gyoza and place the lid on.
Cook until the water has completely evaporated and the wrapper has turned slightly translucent on top – about 3 to 4 minutes.
Use a spatula to transfer onto a plate and serve.