Cut the white part of Napa cabbage into 1/2" width and the leafy part into 1" width. Slice green onions finely. Set aside.
Mix ground pork, salt, and potato starch thoroughly until the mixture becomes sticky.
Bring water to a boil, then drop heaping tablespoon-sized meatballs into the water. Cook the meatballs for a minute until their color changes. Add Napa cabbage, partially cover with a lid, and cook for 3-4 minutes.
Dissolve miso paste in the soup. Just before it comes to a boil, add green onions and stir. Remove from heat and serve immediately.
