Begin by preparing the dumpling filling. In a large bowl, mix together the ground pork, chopped napa cabbage, green onions, minced ginger, mashed garlic, finely chopped mushrooms, and baking soda if you're using it. Add the sesame oil, mirin, oyster sauce, and soy sauce, and combine everything thoroughly using your hands or a fork.
Next, prepare your ramekins or mugs for layering. Start by placing a spoonful of the pork mixture at the bottom of each ramekin, followed by a wonton wrapper. Continue to alternate layers of the filling and wonton wrappers, pressing down gently as you build up the layers until the ramekin is almost full.
Before adding the final layer, pour ⅓ cup of water into each ramekin. Seal it with two wonton wrappers on top.
Place the ramekins into a dutch oven or a large pot, ensuring that the water reaches halfway up the sides of the ramekins. Cover the pot with a lid.
Steam the dumplings for about 20 minutes, or until the pork is fully cooked and the wonton wrappers are soft and tender.
Once done, carefully remove the ramekins from the steamer. Drizzle with chili oil and garnish with sliced green onions before serving warm directly from the ramekin.
