Place the vegetable oil into a deep, heavy-bottomed saucepan and heat until a small cube of bread sizzles and turns golden when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
For the banana fritters, place the flour, baking powder and water into a bowl and whisk together to make a smooth batter.
Dip the banana pieces into the batter to coat, shaking off any excess. Carefully place the banana pieces into the hot oil and deep fry for 3-4 minutes, until crisp and golden-brown. Remove from the oil with a slotted spoon and drain on kitchen paper.
For the chocolate sauce, place all the chocolate sauce ingredients into a small pan over a low heat and whisk together until smooth.
To serve, place the banana fritters into a serving dish with the sauce in a small bowl alongside.