1. Peel sweetpotatoes and cut them into slices. Peel and halve the onions and cut them into even fine slices. Add 500 ml water and 2 teaspoons salt to a bowl and leave to stand for 15 minutes. Then place the onions in a sieve and wash twice thoroughly with water. This will provide a milder taste.
2. Wash the bell peppers and cut them into 2 mm cubes. Cut the fish into 1 cm cubes and keep cool. Wash the coriander.
3. Put the fish stock, lime juice, coriander and paprika in a bowl. Season with salt and chilli (if desired) and put in the fridge for 20 minutes.
4. Remove the coriander and add the fish to the remaining ingredients. Season with salt, pepper and more lime juice.
5. Roast the sweetpotato slices in a toaster or in a pan. Sprinkle with sea salt. Serve the ceviche in a bowl together with the sweetpotato toasties. Sprinkle with lime juice and coriander leaves.