Combine all filling ingredients in a large mixing bowl and mix thoroughly (I mix by clean hand). Cover and refrigerate until ready to use.
Make the dough, Method 1: Place the flour in the work bowl of a food processor with the dough blade. Run the processor and pour the warm water in until incorporated. Pour the contents into a sturdy bowl or onto a work surface and knead until uniform and smooth. The dough should be firm and silky to the touch and not sticky.[Note: it’s better to have a moist dough and have to incorporate more flour than to have a dry and pilling dough and have to incorporate more water).
Make the dough, Method 2 (my mom’s instructions): In a large bowl mix flour with 1/4 cup of water and stir until water is absorbed. Continue adding water one teaspoon at a time and mixing thoroughly until dough pulls away from sides of bowl. We want a firm dough that is barely sticky to the touch.
Both dough methods: Knead the dough about twenty strokes then cover with a damp towel for 15 minutes. Take the dough and form a flattened dome. Cut into strips about 1 1/2 to 2 inches wide. Shape the strips into rounded long cylinders. On a floured surface, cut the strips into 3/4 inch pieces. Press palm down on each piece to form a flat circle (you can shape the corners in with your fingers). With a rolling pin, roll out a circular wrapper from each flat disc. Take care not to roll out too thin or the dumplings will break during cooking. Leave the centers slightly thicker than the edges. Place a tablespoon of filling in the center of each wrapper and fold the dough in half, pleating the edges along one side (see images above).
To boil: Bring a large pot of water to a boil and add dumplings to pot. Boil the dumplings until they float.
To steam: Place dumplings on a single layer of napa cabbage leaves or on a well-greased surface and steam for about 6 minutes.
To pan fry (potstickers): Place dumplings in a frying pan with 2-3 tbsp of vegetable oil. Heat on high and fry for a few minutes until bottoms are golden. Add 1/2 cup water and cover. Cook until the water has boiled away and then uncover and reduce heat to medium or medium low. Let the dumplings cook for another 2 minutes then remove from heat and serve.