Cut the fish into 4cm cubes. Place the fish pieces in a shallow dish
and pour over the fish sauce.
Place the onion, garlic, ginger, turmeric, chili and salt into a
food processor and process until a paste is formed.
Heat the oil in a deep-sided frying pan, carefully add the spicy
paste (at this stage it will splutter), stir it into the oil, lower the
heat and cook gently for about 10 minutes. If the mixture starts to
burn, add a little water.
When the paste is cooked it should be a golden brown color and have
oil around the edges.
Remove the fish pieces from the fish sauce and add them to the pan,
stirring to cover them with the spicy paste.
Raise the heat to medium and cook for about 5 minutes until the fish
is cooked through, turning it so it cooks evenly.
Transfer the fish to a warm serving dish. If the remaining sauce is
very liquid, reduce it over high heat until it thickens, then spoon it
over the fish.
Scatter the coriander over the fish and serve with rice and lemon