Heat oil in a large pan over medium-high heat. Add spring onion, cabbage, mushrooms, carrot, and capsicum, stirring for 5-8 minutes or until cabbage has wilted. Remove from the heat.
Once the vegetable mix has cooled, add bamboo shoots, coriander, ginger, garlic, sesame seeds, sesame oil and soy sauce and stir to combine.
To make dumplings, place wonton wrappers on a flat surface and spoon 2 teaspoons of mixture onto the middle of the wrapper. Line the edge of the wrapper with water. Bring two opposite corners together and pinch at the tip. Bring remaining two corners together to form a pyramid. Pinch all edges together to seal the dumpling. Repeat with all mixture and wrappers.
To freeze the dumplings: Once cooled, freeze the dumplings on the large baking tray, making sure none of the dumplings are touching. Once frozen solid, portion the dumplings into freezer bags or an airtight container
Once defrosted, to steam dumplings, place a steamer lined with baking paper over simmering water. Cook dumplings, for 8-10 minutes or until wonton wrappers look clear.
Serve with fresh coriander and a sprinkle of sesame seeds.