Finely mince the shiitake mushrooms, green onions, ginger, and garlic.
In a medium mixing bowl, combine the ground pork, minced mushrooms, half of the green onions, ginger, garlic, 1 tablespoon of coconut aminos, 1 teaspoon of sesame oil, sea salt, and black pepper.
Place a wonton wrapper in the palm of your hand and spoon about 1 tablespoon of the pork mixture into the center.
Gently squeeze the wrapper around the filling, pleating the sides as you go, and leave the top of the filling exposed.
Line a bamboo steamer basket with the napa cabbage leaves to prevent sticking and arrange the shumai inside without touching.
Place the steamer basket over a pot of boiling water and steam for 10 to 12 minutes until the pork is fully cooked through.
While the dumplings steam, whisk together the remaining coconut aminos, sesame oil, rice vinegar, remaining green onions, and red pepper flakes in a small bowl.
Remove the shumai from the steamer and serve immediately with the zesty dipping sauce on the side.