For the filling, put Ground Beef, cabbage, mushrooms, garlic, green onions, ginger, oyster sauce, soy sauce, cornstarch, sesame oil, and salt into a large bowl. Using your hands, heartily work together all ingredients until very well combined and sticky.

For the gyoza, arrange a small bowl of clean water on a large work surface. Use one wrapper at a time to shape the dumplings individually, covering the remaining wrappers with a towel to keep them from drying out. To shape each gyoza, spread about 1 Tbsp. of the filling in the center of a wrapper, leaving a generous ¼-inch border around the outside. Use a fingertip to dab the edges all around with water. Fold over the wrapper in your hand to form a half-moon, sealing it by starting at one end and crimping the edges together with your fingers, working to the opposite end. Transfer gyoza to a parchment paper-lined sheet tray as done and repeat process until all the wrappers and filling have been used.

To cook the gyoza, heat half of the canola oil in a large skillet over MEDIUM-HIGH heat. Arrange half of the dumplings in the skillet in a single layer, flat side down, and cook until browned on the bottom, 3-4 minutes. Reduce heat to MEDIUM-LOW, carefully add about ½ cup water to the skillet, cover tightly with a lid, and cook until the liquid has evaporated, and the dumplings are cooked through, 5-7 minutes more. Transfer cooked gyozas to a large platter and repeat with remaining canola oil and gyoza.

To make sauce, combine all sauce ingredients in a small bowl with a whisk. Garnish gyozas with green onions and sesame seeds, and serve with sauce on the side.