In a medium bowl, mix the pork with the scallions, ginger, 1½ tablespoons of the soy sauce, 1½ tablespoons of the vinegar, ½ teaspoon of the sesame oil, the salt, and the pepper.

Lightly dust a large baking sheet with flour. Hold one wonton wrapper in your palm, keeping the rest of the wrappers covered with a damp paper towel. Place a barely rounded tablespoon of the filling in the center and fold the wrapper up around the filling, pinching the edges all around to form an open cup (it’s okay if you pinch the wrapper with some of the meat; it doesn’t need to be perfect). Transfer the dumpling to the baking sheet and cover with a damp paper towel. Repeat with the remaining wrappers and filling.

Fill a large saucepan with ¾ inch of water and put a metal steamer basket in the bottom. Lightly oil the steamer basket and then bring the water to a simmer. Add half the dumplings to the steamer basket, cover partially, and steam over medium-low heat until firm, about 8 minutes. Transfer to a small platter and tent with foil. Repeat with the remaining shumai.

Meanwhile, in a small bowl, whisk together the remaining 2 tablespoons soy sauce, 2 tablespoons vinegar, and ½ teaspoon sesame oil. Sprinkle with additional minced scallions and serve with the shumai and sambal oelek.