Prep ingredients: finely chop 1/2 yellow onion, 1 red bell pepper, 4 cloves garlic (minced), 2 teaspoons grated ginger, 2 oz finely chopped button mushrooms (stemmed, 8 pkgs), and either a 1 ounce bag shredded cabbage or 2 cups finely chopped cabbage. Chop 3 scallions finely. Have 1 tablespoon roasted sesame seeds, 1/4 cup soy sauce, 2 tablespoons roasted sesame oil, 1 tablespoon sugar, and 1 1/2 cups panko breadcrumbs ready. Lightly dust a work surface with all-purpose flour. Keep a small bowl of water nearby for sealing wrappers.
Heat a large skillet over medium-high heat and add 1 tablespoon canola oil.
Add the 1/2 yellow onion to the hot skillet and sauté 3–5 minutes, until the onion is soft and translucent.
Add the red bell pepper, minced garlic, grated ginger, and 2 oz finely chopped mushrooms to the skillet. Sauté 5–7 minutes, or until the vegetables have softened.
Add the cabbage (the 1 ounce bag shredded cabbage or 2 cups finely chopped cabbage) to the skillet and cook 1 more minute, stirring to combine.
Remove the skillet from the heat. Stir in the 3 chopped scallions and 1 tablespoon roasted sesame seeds.
In a small bowl, whisk together 1/4 cup soy sauce, 2 tablespoons roasted sesame oil, and 1 tablespoon sugar. Pour this mixture over the cooked vegetables and stir until evenly combined.
Add 1 1/2 cups panko breadcrumbs to the vegetable mixture and stir until the filling holds together but is not wet. Let the filling cool to room temperature or lukewarm before assembling (cooling prevents wrappers from becoming soggy).
Set out the gyoza or wonton wrappers (about 40–50) on a lightly floured surface. Keep unused wrappers covered so they do not dry out.
Working one at a time, place 1 teaspoon of filling in the center of a wrapper. Dip a finger in the bowl of water and brush a thin line of water around the edge of the wrapper. Fold the wrapper over the filling and press the edges firmly to seal, making sure there are no gaps. Shape each dumpling so it has a flat bottom. Place assembled dumplings on a plate and cover loosely with plastic wrap to prevent drying. Repeat until all filling is used.
To cook the potstickers, heat a large nonstick pan over medium-high heat and add 1 tablespoon canola oil (add more oil as needed between batches).
When the oil is hot but not smoking, arrange dumplings flat side down in the pan in a single layer, not touching. Fry 1 minute, until the bottoms are light golden brown.
Carefully pour 1/4 cup water into the pan and immediately cover with a tight-fitting lid. Reduce heat to medium and steam the dumplings for 3 minutes.
Remove the lid and continue cooking about 1 minute, until any remaining liquid has evaporated and the bottoms are crisp. Cut one dumpling to confirm the filling is heated through.
Transfer cooked potstickers to a plate. Wipe the pan clean with paper towels (or wash) and repeat steps 11–14 with remaining dumplings, adding more oil as needed.
For the dipping sauce: in a small bowl stir together 1/4 cup rice vinegar, 1/4 cup soy sauce, 2 teaspoons honey, 2 teaspoons chili garlic sauce, 2 teaspoons sesame oil, 1 green onion (minced), 2 teaspoons minced ginger, and 1 teaspoon freshly grated orange zest (optional).
Serve the potstickers warm with the prepared dipping sauce.