Bring a large pot of water to a boil and blanch the cabbage leaves for 2 minutes until pliable, then immediately shock in ice water and pat dry.
Finely mince the shiitake mushrooms, green onions, and garlic.
In a large mixing bowl, combine the ground beef, minced mushrooms, green onions, grated ginger, garlic, 1 tablespoon of coconut aminos, sesame oil, salt, and pepper.
Lay each cabbage leaf flat on a cutting board and carefully shave down the thick center rib so it is flush with the leaf.
Place approximately 2 tablespoons of the beef mixture into the center of each leaf, fold in the sides, and roll tightly like a small burrito.
Arrange the dumplings in a steamer basket lined with parchment paper, ensuring they do not touch.
Steam over boiling water for 10 to 12 minutes until the beef is cooked through and the cabbage is tender.
Serve the warm dumplings immediately with the remaining tablespoon of coconut aminos for dipping.