In a large bowl combine the pork, cabbage, half of the scallions, mushrooms, bok choy, bamboo shoots, garlic, ginger, soy sauce, corn starch, and sesame oil. Mix well.
Lay one dumpling wrapper on a dry, clean surface and place a tablespoon of filling in the center. Dip your finger in a cup of water and run it along the edges of the dumpling wrapper. Fold the wrapper over and press along the edges and crimp them tight to seal them shut. Repeat with the remaining wrappers. Set aside on a plate or sheet pan for 5 minutes.
Bring a large saute pan 1/4 of the way filled with water to a low simmer. Place the dim sum in a single layer in the pan (in batches if needed, not to overcrowd the pan) and cover with a lid. Steam for approximately 8 minutes or until the internal temperature reaches 155 degrees using a thermometer. Remove with a slotted spoon onto a paper towel to drain any excess water.
For the sauce: In a sauce pan on low heat whisk together all ingredients except water. Warm the ingredients, whisk in water a little bit at a time until the sauce is smooth. Serve warm to dip in. Garnish with the remaining chopped scallions.