Combine lime zest, juice and sugar in a bowl. Wash coriander well, finely chop root and stem and roughly chop leaves. Add coriander, cucumber and kaffir lime leaves to lime juice and set aside.
Place coconut milk and lemongrass in a wok or saucepan and bring to the boil. Add fish, cover and reduce heat to simmer. Cook for 10 minutes or until cooked through.
Remove fish from pan, discard lemongrass. Stir Five Tastes Curry Paste and fish sauce into coconut milk, cook for 1-2 minutes.
Ladle curry sauce into the base of serving bowls, place fish on sauce and top with cucumber mixture. Garnish with fried ginger.