Knead the flour with the oil, vinegar, 125 ml of water and a pinch of salt into a smooth dough and place it in the refrigerator for about 1 hour, wrapped in cling film.
Remove the shells from the crab tails, remove the intestines, chop the meat and season with oyster sauce and a little bit of pepper and salt. Clean the Chinese cabbage, chop it and fry it in a frying pan with 2 tbsp of peanut oil, season with pepper and salt and let it cool down a little bit.
Briefly fry the crab tails in a frying pan with 1 tbsp peanut oil, remove, mix with the Chinese cabbage and cool the whole thing.
Put the chicken soup in a saucepan and heat.
Roll out the dough thinly and cut into 15 cm squares. With a tsp put a small amount in the middle of the dough pieces form and all around a border of about 2 cm. Then, at all four ends, carefully pull the dough pieces into the center and press well at the top, so that you get a pocket (bag). Cook the pouches in the chicken soup for about 8 minutes or in a steam basket and cook over steam. Clean the white cabbage and peppers and cut them into thin strips. Spread them evenly on the plates and mix the ingredients for the two sauces. Arrange the dumplings on the white cabbage and bring the sauces to the table.