Cut the fish fillet into 2-3 cm cubes and drizzle with a little lemon juice.
Peel the pineapple and cut into cubes, peel the mango as well, cut along the stone and dice. Cut out the hard central ribs of the kaffir lime leaves and cut the leaves into very fine strips.
Briefly toast the curry paste in a dry pan or in a wok, pour in the coconut milk, add the lime leaves and simmer for 5 minutes. Then mix in the fish, pineapple and mango and simmer for another 10 minutes more than simmer.
Season with the fish sauce and possibly a little lemon juice and serve with basmati or glutinous rice.