Sift over the gluten free self raising flour, baking powder, xanthan gum and add the lemon zest. Mix until well combined.
Pour the mixture into the prepared loaf tin and smooth the surface. Bake for 45 minutes or until a skewer inserted into the middle comes out clean
Carefully poke holes all over the cake with a skewer (to allow the lemon drizzle to soak in). Pour the lemon drizzle over the top of the cake