Heat the oven to 180°C (350°F, gas mark 4). Brush a 22 cm (8½ in) round cake tin with oil. Line the base with baking paper and sprinkle it with sugar. Arrange the pears in the base in a wagon wheel pattern.
To make the batter, sift together the flour, bicarbonate of soda, cinnamon and ginger. Heat the milk, sugar and treacle together, stirring until the sugar has dissolved. Beat together the egg and oil, then stir them and the milk mixture into the flour, beating well to give a smooth texture.
Tip the mixture over the pears and bake for 35-40 minutes until risen and firm to the touch.
Run a knife around the edge of the pudding and turn it out onto a plate. Serve hot, with custard or yoghurt.