Stir together the chicken, leeks, garlic, ginger, scallions, soy sauce, dark soy sauce, oyster sauce, bouillon, sugar, and black pepper in a large bowl. Set up your dumpling station: Fill 1 small bowl with the ¼ cup water, and have your wrappers and a spoon in the dumpling-mixture bowl nearby. Place 1 tablespoon of the filling on the center of 1 dumpling wrapper. Dip your finger in the water, then wet half of the wrapper rim with your finger. Fold the dry side up and over to meet the wet side, then crimp together tightly with your fingers until the wrapper stays closed. Repeat with the remaining filling and wrappers. Add the dumplings to a large pot of boiling water, and cook until they float, about 7 minutes. Serve with some chili oil, soy sauce, and black vinegar. Enjoy!
