You can sometimes order banana leaves from a good Asian or exotic greengrocer. If that fails wrap the fish in foil or greaseproof paper.
First, make the dipping sauce. Heat the sesame oil in a pan and fry the chilli, ginger, lemon grass and lime leaves slowly with the garlic for 1 minute to soften and release the flavours. Add both soy sauces, bring the mixture to the boil, then cool and pour it into a bowl or, ideally, individual soy dishes.
Now for the rice: simmer the lemon grass with the lime leaves in the salted wat