Mix together the soy, oyster sauce, mirin, chilli, garlic, and cornflour.
Add the chicken and leave to marinade for at least 20 minutes and up to 8 hours
Heat the oil in a non-stick wok till smoking slightly
Add all the diced vegetables and stir-fry for 2 minutes
Add the chicken and marinade and stir-fry for a further 2-3 minutes till the chicken is cooked and the sauce is thickened. If necessary add water to keep the sauce thick but not burnt.
Put a tablespoon of the mixture into the centre of each iceberg lettuce leaf and if you like, garnish with a little fresh coriander
Wrap up into a roll and eat with your fingers