How to Make It
Cut the chicken into 1/4-inch pieces and spread on a baking sheet. Freeze until firm but not frozen, 40 minutes.
In a food processor, in 2 batches, pulse the chicken until coarsely ground.
In a bowl, cover the mushrooms with boiling water and let stand for 15 minutes. Drain and squeeze out any excess water, then finely chop.
In a large bowl, combine the ground chicken with the mushrooms and all of the remaining ingredients except the cornstarch, dumpling wrappers and canola oil; fold gently to combine. Fold in the cornstarch just until incorporated.
Lay a wrapper in the palm of one hand. Using your finger, brush the outer edge with water. Spoon 1 heaping tablespoon of filling in the center. Fold the wrapper over the filling to form a half-moon; pinch at the top to adhere. Fold a pleat in the wrapper on the top left, angling back toward the center. Press with your fingers to adhere. Repeat the pleating on the top right of the wrapper to meet the first pleat in the center. Transfer the dumpling to a parchment paper–lined baking sheet and cover with plastic wrap; repeat with the rest of the wrappers and filling.
Pour enough canola oil into a large nonstick skillet to cover the bottom. Arrange some of the dumplings in the skillet with a non-pleated side down (you will need to work in batches). Cook over low heat until golden on the bottom, about 3 minutes.
Carefully pour in enough water to reach halfway up the dumplings. Cover and cook until almost all of the water is absorbed and the filling is cooked through, about 4 minutes. Uncover and cook until all of the liquid has evaporated and the dumplings are crispy on the bottom, about 2 minutes longer. Carefully invert onto a plate. Repeat the process with the remaining dumplings. Serve warm.