First, make the relish. Scoop seeds from the cucumber, thinly slice on the diagonal and place in a bowl. Add chilli and shallot, toss to mix and set aside. Place lime juice, sugar and water in a small pan and bring to a simmer, stirring well to dissolve the sugar. Simmer until slightly thickened. Cool. Put all fishcake ingredients, except the beans and oil, into a food processor and pulse to a finely chopped mixture. Do not overprocess as you want to keep some texture to the fishcakes. Scrape the mixture into a bowl and stir in the beans. With wet hands, shape the mixture into small patties about 5cm (2in) in diameter. Heat a 2-3cm (1-1½in) depth of oil in a deep frying pan or wok. Fry patties in batches for 1-2 minutes on each side, until golden brown. Drain on a tray lined with kitchen paper and keep warm. When the fishcakes are all cooked, pour dressing over the relish and stir in the chopped herbs. Serve the fishcakes hot, with the relish on the side.