In a large mixing bowl, combine the chopped onion, parboiled napa cabbage, bean sprouts, finely chopped tofu, and soaked noodles. Add the large egg, along with a sprinkle of salt and freshly ground black pepper, to bind the mixture.

In a separate bowl, mix the minced garlic, sesame oil, and soy sauce. Stir well to create a fragrant sauce that enhances the filling's flavor. Pour this aromatic mixture over the vegetable blend in the first bowl.

Lay out a round dumpling wrapper on a clean surface. Spoon about one tablespoon of the prepared filling into the center of the wrapper. Moisten the edge of the wrapper with a little water to seal. Fold it over to form a half-moon shape, and press the edges firmly together.

Continue the assembly process with the remaining dumpling wrappers and filling. Lay each assembled Veggie Mandu on a parchment-lined baking tray.

Choose your preferred cooking method: steam for about 10 minutes or pan-fry for 3-4 minutes on each side until golden brown.

Once cooked, transfer Veggie Mandu onto a serving platter. Serve them warm with a dipping sauce made from soy sauce, vinegar, and chili flakes.