Chop all the marinade ingredients in a mini-chopper, then empty them into a bowl.
Slice the steak across into thin strips, then add these to the bowl, pushing them down well into the marinade. For the dipping sauce, mini-chop all the ingredients, give them a good burst, then pour into a bowl.
To cook the steak, heat a frying-pan lightly brushed with oil till very hot, then add the strips of steak. Cook for 30 seconds, then flip them over with a fork and spoon (or tongs) and give them another 30 seconds before transferring to a warm serving dish.
To serve: roll up strips of steak, shredded spring onion, cucumber and coriander in the lettuce leaves, swirling them in the dipping sauce - and have plenty of paper napkins handy.