In a small bowl, combine the cabbage and salt. Set aside for a few minutes. After some time, drain the excess water from the cabbage.
Add the pork, garlic, leek, ginger, pepper, sesame oil, and soy sauce to the cabbage. Mix thoroughly.
Sprinkle the flour on top of a flat surface.
Wet the edges of the wrapper with water. Take a little more than 1 tsp of the mixture and put it in the center of a gyoza wrapper.
Seal the mixture by crimping the sides of the gyoza wrapper. Set aside on the floured surface while making the rest of the gyoza.
Heat the oil in a frying pan over medium heat. Arrange the gyoza on the pan, about 12 of them. Slightly overlap each gyoza.
Fry for 2-3 minutes over medium heat, or until the bottom of the gyoza is golden brown.
Add the 1/3 cup of water and cover the frying pan. Cook until the water evaporates and the gyoza top turns translucent.