In large skillet or a wok heat the vegetable oil until hot. Add the shrimp, onion, carrot, cabbage and mushrooms and quickly stir fry while combining the ingredients. Add the pepper flakes, sesame oil, soy sauce, vinegar and sugar, adjust the seasoning and pour out onto a cookie sheet to cool. When the mixture is cool, begin making the potstickers. Lay out one wonton, brush the edge with water and put 1 teaspoon of the filling into the middle of the wonton. Fold the edge over on the diagonal to form a packet. Trim the edges to eliminate any square corners. Dust the finished potstickers with a light coating of cornstarch to prevent sticking before cooking. Potstickers may be frozen at this point.
Using a bamboo steamer over a wok or pot, heat 1 cup of water to a boil. Place the potstickers in the oiled steamer basket and steam them until the dough becomes translucent, about 3 minutes. Remove from the basket and proceed to the skillet cooking process.
Heat a non-stick skillet with 3 tablespoons vegetable oil. When the pan is hot, add enough potstickers to cover the bottom of the pan, but do not crowd them. Cook both sides until well browned and crisp. Continue in this manner until all of the potstickers are cooked. Keep them warm in a low oven while finishing the last batches. Serve with sweet mustard dip.
Sweet mustard dip:
Combine water, honey, vinegar, soy and mustard in a saucepan over low heat. Cook for 3 to 4 minutes to blend the flavors. Remove from the heat, let cool for several minutes until just warm and serve with potstickers.