Combine the lemon juice, dried chilli, onion rings, garlic and seasoning in a large pitcher.

Arrange the fish pieces in a shallow porcelain dish and pour the lemon juice over them. (Add more lemon juice if the mixture does not completely cover the fish pieces.) Cover the dish and transfer it to the refrigerator. Leave for at least 3 hours, or until it is opaque and white.

About 30 minutes before serving time, bring 1 3/4 litres (3 pints) 7 1/2 cups of water to the boil in a large saucepan. Put the sweet potatoes into the pan and cover. Reduce the heat to moderate and cook for 30 to 35 minutes, or until they are cooked through and tender.

While the potatoes are cooking, arrange a bed of lettuce leaves on individual serving plates.

Remove the pan from the heat and drain the potatoes. Peel and cut each one into three slices. Keep hot while you cook the sweetcorn.

Pour 1 1/4 litres (2 pints) (5 cups) of water into a saucepan and bring to the boil. Drop the corn rounds into the pan and boil for 4 to 5 minutes or until they turn bright yellow. Remove from the heat and drain the corn.

Remove the marinated fish from the refrigerator and divide it equally between the plates. Garnish with the onion rings and strips of fresh chilli pepper. Arrange the sweet potato slices and corn rounds around the fish and serve at once.