Thinly slice the leeks place in a large sieve and rinse under cold water to remove any grit. Drain well.
Cut out 4 large squares of heavy-duty foil grease lightly with a little oil and then divide the leeks placing in the centre of piece of foil. Scatter half of the coriander over. Place a salmon fillet on top of each season.
Mix together the remaining oil curry powder and lemon juice and pour some over each steak allowing it to drizzle over the fish onto the bed of leeks. Season with salt and freshly ground black pepper then fold the foil over and seal the packages.
Put the packages on the grilling rack of a preheated barbecue and cook for 15 minutes. Halfway place the stems of vine tomatoes on the barbecue and cook alongside the salmon (cooking time will depend on the temperature of barbecue and whether the barbecue is used open which will take slightly longer than with a lid). To cook the salmon parcels in the oven heat the oven to 200C/400F/gas mark 8. Place the parcels on a baking tray and cook for 15 minutes. Unwrap one parcel and test the fish is cooked using the point of a knife.
Remove the packages and either serve immediately in or out of the foil. Scatter the remaining chopped coriander over the fish and serve with the tomatoes to accompany. Alternatively allow to cool then remove the wrappings and serve cold.