Peel 2 cloves of garlic and put them into the bowl of a food processor. Peel away and discard the outer leaves of a stalk of lemon grass, cut the tender stem into short lengths and add to the garlic. Peel a 30g piece of ginger and add to the bowl with 20g of coriander leaves and stalks.
Process the garlic, lemongrass, ginger and coriander leaves to a paste then add 150g of tomatoes and process briefly to a wet paste. Season lightly with 1 tbsp of fish sauce and 3 tbsps of groundnut oil.
Heat an overhead grill, then place a 450g piece of salmon on a foil-lined grill pan. Spread the paste over the surface of the salmon then place under the grill, a good 20cm from the grill, and leave it to cook, watching carefully, for about 15-20 minutes.
When the fish is done, remove from the heat. Break it into big, juicy flakes then divide between four curls of iceberg lettuce leaves. Add a couple of mint leaves and some watercress to each, fold the lettuce leaves over the fish and eat with your fingers.
The trick
Keep an eye on the fish as it grills as the spice paste burns easily. Take care not to overcook the fish – it should be only just opaque inside. The fish should be a middle piece from the fillet if your cut is from the thick end or from the thinner, tail end, then adjust the cooking time accordingly.
The twist
Instead of grilling the salmon, bake at 200C/gas mark 6 for 15 minutes or so, until the surface has lightly browned. Rather than using the lettuce wrap, serve in two large pieces, with green vegetables, or serve cold, as the filling for a wrap or bun with crisp salad leaves.
