Place ground pork in a large mixing bowl and stir until softened and sticky. Add watercress, ginger, sesame oil, shoyu, and egg white; mix well. Place 1 teaspoon filling in center of each wrapper; dampen edges slightly. Fold wrapper over 1/3 of way and 1/3 of way on the other side, overlapping the wrapper over the filling. Join the unfolded ends by fluting the edges-it should look like the shape of a purse.
Place 1 tablespoon vegetable oil in skillet and heat. Place potstickers in rows in skillet (about 16 pieces). Pour 1/2 cup water in skillet and cover. Cook for 8 minutes or until the water has evaporated. Repeat until all potstickers are cooked. Makes about 4 dozen.
Approximate Nutrient Analysis per potsticker:
80 calories, 5 g fat, 1.5 g saturated fat, 10 mg cholesterol, 135 mg sodium, 4 g carbohydrate, 0 g fiber, 0 g sugar, 3 g protein