Finely chop and squeeze juice from kimchi.
Blanch the bean sprouts in boiling water, drain, chop, and squeeze out water.
Squeeze out water from the tofu. Using a cheesecloth will make squeezing easier. Finely chop the noodles. Finely chop the onion and squeeze out water. Finely chop the scallions.
Combine all the filling ingredients in a large bowl.
Place one heaping teaspoonful to a tablespoon of the filling on a wrapper. Wet the edges of the wrapper with water or egg wash and seal tightly (pushing the air out with your fingers) into a half-moon shape. (Please feel free to use it here for a half-moon-shaped dumpling. Then, bring the two ends together, apply water or egg wash to one end and press tightly to create a round shape. Repeat this process until all the filling/wrappers are used.
Kimchi mandu can be steamed for 10 minutes in a steamer (12 minutes if frozen). Line the steamer with a wet cheesecloth, paper towel, or cabbage leaves to prevent the mandu from sticking.
Enjoy with soy sauce or by itself.