Put the whiting, beans and basil in the food processor and whizz until just combined - you don't want it too smooth. Remove to a bowl and add the fish sauce, curry paste, lemon rind, sugar and black pepper. Mix well then add in the beaten egg. Shape into 8 fish cakes 2-3 cm thick.
Heat the oil in a large frying pan and add in half the fish cakes. Fry gently until golden and cooked through. This will take about 10 minutes. Cover with tin foil and keep warm while you cook the remaining fish cakes.
Meanwhile make up the sauce by putting the rice wine vinegar, sugar, chilli, salt and garlic in a saucepan. Chop up the coriander stalks and add them to the saucepan. Keep the leaves to use later.
Heat gently until the sugar melts. Combine the water and cornflour and stir it into the mixture. Gently simmer until the sauce thickens. Set aside to cool then add in the cucumber and the chopped coriander leaves.