Make the batter by mixing the flour, baking powder, sugar, salt and coconut in a bowl. Add the measured water and mix it with a fork or spoon until smooth.
Heat 7 cm (3 inches) of oil in a nonstick wok over a medium heat. While it is heating, peel the bananas or plantains, cut each banana into half lengthways, then cut them into 5 cm (2 inch) slices. Halve the plantains lengthways and then slice each length in half. The oil is ready when a little batter sizzles when dropped in.
Coat the banana slices with the batter and then lower them carefully into the hot oil, 6–7 pieces at a time. Cook the bananas over a medium heat for 6–7 minutes until golden brown. Remove the fritters from the oil with a slotted spoon and drain on kitchen paper.
When all the slices are cooked, arrange them on a serving dish and serve at once, sprinkled with sugar, if liked.