Cut the fish into 3 cm cubes. Place the fish pieces on a plate and
sprinkle with the salt and turmeric. Set for 10 minutes.
Trim the lemon grass stems to about 18 cm long. Bruise the white
fleshy ends so that the fragrance will be released during cooking, and
tie the stems into loops.
Heat the peanut oil in a large pan; add the onion and cook over
medium heat for 10 minutes, or until soft and lightly golden
Add the garlic and ginger and cook for about 1 minute.
Add the fish, paprika and rice flour and combine well.
Pour in the water, coconut milk and fish sauce, and stir.
Add the loops of lemon grass and simmer for 10 minutes, or until the
fish is cooked.
Cook the noodles in a large pan of boiling water for 8 to 10 minutes
or until tender, then drain.
Place a mound of noodles in 8 warm individual serving bowls and
ladle over the fish soup.
Offer the garnishes in separate small bowls so the diners can add
them to their own taste.