Finely chop the cabbage, mushrooms, carrots, and spring onions. Try to keep the vegetables small and evenly sized so they fit easily inside the dumpling wrappers.
Heat vegetable oil in a skillet over medium heat. Add the mushrooms and cook for 3–4 minutes until softened and their moisture has mostly evaporated.
Add the cabbage and carrots. Cook for another 3–4 minutes, stirring occasionally, until the vegetables soften slightly. Stir in the garlic and ginger. Cook for about 30 seconds until fragrant.
Add the spring onions, soy sauce, sesame oil, rice vinegar, and black pepper. Mix everything well and cook for another minute. Remove the filling from the heat and allow it to cool completely before assembling the dumplings.
Dip your finger into a small bowl of water and lightly moisten the edges of the wrapper. Fold the wrapper in half over the filling to create a half-moon shape.
Press the edges together firmly to seal. You can make small pleats along one side for a traditional dumpling appearance. Repeat with the remaining wrappers and filling. Keep the prepared dumplings covered with a clean, slightly damp kitchen towel to prevent them from drying out
Line a steamer basket with parchment paper and make a few small holes for steam circulation. Arrange the dumplings in a single layer, leaving a little space between each one.
Bring water to a boil in a pot and place the steamer basket over it. Cover and steam for 8–10 minutes, or until the wrappers become tender and slightly translucent.
For crispy-bottomed vegetable dumplings, heat vegetable oil in a nonstick skillet over medium heat. Arrange the dumplings in the skillet and cook for 2–3 minutes until their bottoms turn golden brown.
Transfer the cooked vegetable dumplings to a serving plate. Sprinkle with toasted sesame seeds and chopped spring onions. Serve warm with soy sauce, chili oil, or a simple mixture of soy sauce and rice vinegar.
