How to Make It
In a colander, toss the zucchini with 1/2 tablespoon of salt and let stand for 30 minutes. Rinse the zucchini under cool water; squeeze and pat dry. Transfer to a medium bowl. Add the pork, celery, scallions, soy sauce, Chinese cooking wine and 1 tablespoon oil; mix well.
Line a large baking sheet with wax paper. On a work surface or in your palm, moisten the edge of 1 gyoza wrapper with water; keep the rest of the wrappers covered with a damp kitchen towel. Spoon a level teaspoon of the pork filling into the center of the wrapper. Fold the wrapper over the filling to form a half-moon. Pinch the wrapper in the center, then pleat the edges to seal. Transfer the dumpling to the prepared baking sheet and cover with a damp kitchen towel. Repeat with the remaining wrappers and filling.
Line a large steamer basket or several bamboo steamer trays with damp cheesecloth or lettuce leaves. Arrange the dumplings, not allowing them to touch, in a single layer on the cheesecloth. Set the steamer basket over 1 inch of simmering water in a large saucepan. Cover and steam until the filling is cooked through and the wrappers are tender, 10 to 15 minutes. Serve at once.
Heat a very thin film of vegetable oil in each of 2 large nonstick skillets. Arrange the dumplings in the pans, pleated sides up, in concentric circles: do not overcrowd the pans. Add enough water to reach halfway up the sides of the dumplings and bring to a boil. Cover partially and cook until the water has evaporated and the dumplings are crisp and browned on the bottom, about 15 minutes. Serve at once.
You can easily freeze dumplings: Spread the uncooked dumplings on a parchment-lined baking sheet, cover the sheet with plastic wrap and freeze until the dumplings are firm, at least 4 hours. Store the frozen dumplings in sturdy freezer bags. Steam or pan-fry the dumplings per the recipe, but increase the cooking time by a few minutes. For the pan-fried version, add more water if the pan dries out before the dumplings cook through.