In a small bowl, whisk together 1 tsp sesame oil, soy sauce, and vinegar. Set aside.
Line a rimmed baking sheet with parchment paper and sprinkle with flour. Set aside.
Put remaining 4 tbsp sesame oil, along with the pork, garlic chives, mushroom powder, cornstarch, salt, ginger, and pepper, into a medium bowl and stir vigorously with a rubber spatula to combine.
Working with one wrapper at a time, put a tablespoon of pork filling onto a wrapper, fold wrapper in half, and seal it with water, Transfer each dumpling to reserved baking sheet and cover with a dish towel.
While you are making the dumplings, bring a 5 qt pot of water to a boil. Working in three batches, boil dumplings until filling is cooked through (about 8 minutes).
Using a slotted spoon, transfer dumplings to a platter and serve with reserved dipping sauce.