Remove and discard the core and outer leaves from the cabbage, undo the remaining cabbage leaves and place them in a pan of salted boiling water for 2 minutes to soften. Cool them in a bowl of cold water, drain and put to one side.
In a food processor, whizz up your garlic, ginger, spring onions, coriander, chilli and fish sauce with a good pinch of salt. Then add the chicken, water chestnuts, lime zest and juice and sesame oil and pulse until you have a minced meat consistency.
Place a heaped dessertspoonful of the flavoured mince on to one end of each cabbage leaf. Fold it up and tuck in the sides, then roll up. Rub a bamboo steamer, colander or normal steamer with a little olive oil and place in the cabbage parcels. They may try to unfold themselves, but once you start putting them next to each other they will hold in place. When they're all in, sit the steamer over a pan of boiling water, making sure the water doesn't touch the parcels and that it's just the steam that's cooking them. Put a lid on top and steam for about 6 minutes until cooked. If you're worried about the cooking time, take one of the parcels out and cut it in half to make sure that the heat has penetrated and that they're cooked.