Add about 1/2" of water to a large stock pot that will comfortably hold a bamboo steamer. Line the steamer baskets with cabbage leaves and place buns on the leaves. Depending on the size of your steamer, you may need to do several batches.
Stack the bamboo baskets on top of each other and secure with the lid. Bring the water to a boil in the pot and carefully set the bamboo steamer into the pot. Cover with the lid and steam the buns for 7-8 minutes or until puffed and light.
Divide the slow roasted pork between the buns and top with a sprinkle of carrot, radishes, pickled onions, cilantro, green onions and sesame seeds. Drizzle reserved dipping sauce over the buns and enjoy immediately.