Common recipes for potsticker/wonton-style (thin wrapper) dumplings use egg as a binder for the filling, to make it easier to work with and to displace air. For comparison, if you make a filling with no binder, it will be hard to place without getting bits of it in the way of sealing the dumpling, and there tends to be too much air inside causing oil ingestion if fried, bad heat transfer if steamed, and bloating/water ingestion if boiled.
Legume flours, flaxseed and other binders good in baking have the issue that they need some cooking time to set - typically longer than you can cook a dumpling. Starch-thickened sauces would be a possibility but the result will be likely too much on the gloopy side.
What non-animal ingredient works well to fill this gap without weighing the filling down too much?