Soak mung beans for two hours in warm water or overnight in cold water, then drain. Transfer to a large pot, add 1 tsp salt and fill water until it's just covered. Bring to a boil, then lower to medium low to simmer, stirring occasionally. Once the water is mostly gone (15-20 minutes), bring down to the lowest heat possible and cover, allowing the beans to soak up the remaining water and soften completely. Mash with a potato masher or with the back of a spoon until it's the consistency of mashed potatoes.

To make the onion oil, gently heat 1/3 cup vegetable oil with sliced onions to get the onion flavour. Cook until the onions are soft and falling apart, about 15 minutes. Strain out onion to add to the cooked mung beans. Similarly, make the green onion oil by gently heating the oil then removing from heat (about 3 minutes) for the onions to cook.

Remove mung beans from heat after 25-30 minutes. Add the strained onions (there'll still be some oil which is good. There should be 1-2 tsp of oil with the onions) and 1 tsp black pepper. Mix until incorporated. Roll into 1 inch balls and set aside.

To make the dough, mix together glutinous rice flour, salt and 3 tbsp onion oil. Add water 1/2 cup at a time until a dough forms. It should be a little tacky, but not stick to your fingers.

Take about 2-3 tbsp sized chunks of the dough and pinch out to just under 1/4 inch thickness to make 3 inch circles (the dough is too tacky and delicate for rolling pins). Wrap the 1 inch bean balls until covered, pinching off any excess dough. Use oil on your hands to keep the dough from sticking, and add a little extra water if you find the dough gets dry or crumbly.

When the dumplings are all made, cook them by boiling a large pot of water with 1/2 tsp of salt and 2 tbsp of regular oil (not onion oil). Once at a rolling boil, cook the dumplings in batches, gently stirring occasionally to keep the dumplings from sticking together. Wait until they float to the top for about a minute or two before removing from the water.

Remove and let cool briefly in a bowl of ice water, then drain. Arrange on a lightly oiled plate (using the onion oil), and drizzle some onion oil overtop so they don't stick together.

To serve, add the green onion oil on top with some vegetarian dipping sauce. Store in an airtight container for up to a week =)