For the filling: Place the Napa cabbage in a strainer and sprinkle with ¼ teaspoon of kosher salt, let it sit for 20 minutes. Using a cheesecloth, strain the cabbage to remove and discard as much liquid as possible.
Combine all the ingredients in a large mixing bowl, just until combined. (Be careful not to over mix, the pork fat will begin to melt.)
For the Yaki Gyoza: Place one gyoza skin on a clean wooden cutting board. Dipping your index finger into water and trace along the edges of the skin.
Fill with 1 teaspoon of the gyoza filling in the center of the skin and seal the edges of the dumpling (it resembles a half moon), pleating in edges as it meets the other. Place on a parchment lined cookie sheet. Repeat until all of the filling is used.
Using a non-stick pan, heat one tablespoon of sesame oil on medium. Working in batches of 8, add the dumplings into the pan and fry the bottoms until golden brown.
Pour in 2 tablespoons of water and cover with a lid. Steam the dumplings for 5 minutes, or until the internal temperature of pork reaches 165°F. Repeat with remaining dumplings. Remove from the pan and serve.
For the sauce: Combine all ingredients in a bowl and whisk. Serve immediately.