Preheat the barbecue so it’s hot, or until the coals turn white.
Rinse the fish under cold water and pat dry with kitchen paper.
Twist the stalks off from the bunch of coriander and place in a pestle and mortar, keeping the leaves for the garnish. Remove the tough outer leaves from the lemongrass, trim and add to the mortar.
Peel, slice and add the garlic and ginger, then slice and add the chilli (if using). Add the lime leaves, then bash them a bit to release the flavours.
For each trout, take a large double sheet of newspaper and line with greaseproof paper.
Slice 3 limes, then place a line of the slices in the middle of each newspaper. Lay the fish on top and stuff the cavity with half the herby mixture, season with sea salt and drizzle with oil. Top with more lime slices and drizzle with more oil and salt.
Wrap up the newspaper and tie with string. Dunk both parcels in a bucket of water and leave to soak for no more than 5 minutes.
Barbecue the fish parcels, uncovered, for 30 minutes or until the flesh is firm. The newspaper will be black, but don’t worry – the important thing is that the fish will be cooked to perfection.
Remove the fish from the paper, drizzle with any juices, top with coriander leaves and serve with lime wedges.