1. Preheat oven to 180 ºC/350ºF/Gas Mark 4.
2. Grease and flour a tin.
3. Sift the flour, baking powder, cocoa powder, bicarbonate of soda and sugar.
4. Grate lime and courgette.
5. Beat the egg with the vegetable oil.
6. Mix the egg and oil into dry ingredients and stir in gated courgette and lime.
7. Pour batter into tin and bake for 25- 30 minutes.
8. Dust with icing sugar.
9. Serve.