Heat oil in a large nonstick skillet over medium-low heat.

Add onions and cook until translucent (about 5 minutes), stirring occasionally.

Add ginger and garlic; cook until softened (about 1 minute), stirring.

Add tofu, increase heat to high, and cook, stirring constantly, until tofu is dry and golden brown (about 5 minutes).

Add soy sauce and sesame oil; cook until liquid evaporates.

Turn off heat.

Stir in scallions, cabbage, carrots, cilantro, salt, and pepper.

Place filling in a strainer and cool for 10-15 minutes.

Squeeze out excess moisture.

Place mixture in a large bowl, add egg, and mix thoroughly.

Fill a small bowl with cold water.

Place a dumpling wrapper in your hand.

Spoon 1 tablespoon of filling into the wrapper.

Use your finger to rub water along the edge of the wrapper.

Fold in half to enclose the filling, pressing the edges to seal tightly.

Repeat for remaining wrappers and filling.

Line a bamboo steamer with cabbage leaves.

Arrange dumplings in a single layer (not touching).

Cover the steamer with a tight-fitting lid and cook over a water bath until filling is firm and wrapper is translucent and slightly gummy (15-20 minutes).

Depending on steamer size, you may need to do this in batches.

For the sauce: Combine soy sauce with sliced scallions.

Serve dumplings immediately with dipping sauce.