Cut fish fillet into finger-sized pieces. Lightly season with salt and pepper.
Combine self-raising flour in a large mixing bowl, add in rice flour, salt and pepper. Make a well in the centre and add egg and chilled soda water. Mix well with a balloon whisk into a smooth batter. (Add a little chilled water, if necessary.)
Heat wok with enough oil. Coat fish slices with a little flour. Shake off excess flour, then dip the slices into batter. Allow excess batter to drain off, then put into the hot oil over medium-high heat.
Deep-fry the fish slices in batches until golden and crispy. Remove and drain oil. Serve the crispy fish slices with chilli sauce immediately.