Preheat the oven to 200C/gas mark 6 and line a standard, 1lb loaf tin with baking parchment. Set aside.
In a bowl, mix the self raising flour, sugar, baking powder, vanilla extract and lemon zest. Add the oil, lemon juice and 160ml of cold water, and mix until smooth.
Once combined, pour the entire mixture into the lined tin and bake in the middle of the oven for 30 mins or until a skewer comes out clean.
Once baked, let it cool in the tin for around 10 mins, before removing and transferring onto a wire rack. Let it cool completely.