Preheat oven to 180°C/160°C/Gas Mark 4. Grease and line a 900g loaf tin. Place the flax seed and water in a jug mix, set aside for 10 minutes to thicken.
Cream together the margarine, coconut milk and sugar until smooth. Add the lime zest and mix. Once the flax seed mixture has thickened to the consistency of an egg pour into the mixture and stir through until the mixture is smooth.
Sieve the flour and Baking Powder on top and fold in to the mixture. Finally add the desiccated coconut and fold through the mixture.
Pour the mixture into the prepared loaf tin and place in the oven. Bake for 1 – 1:15 hours, until golden brown and a skewer inserted into the centre of the sponge come out clean. Leave to cool in the tin for 20 minutes and then place on a wire rack to cool completely.
Once the cake has cooled, melt the chocolate, break the chocolate into pieces and place in a microwaveable bowl. Place the chocolate in the microwave and heat for 30 seconds, stir and heat in 10 second bursts, stirring between each burst until the chocolate is melted.
Pour the melted chocolate over the top of the loaf cake and using the back of a spoon push the melted chocolate to the edges of the loaf to completely flood the top of the cake.
Sprinkle the lime zest and desiccated coconut on top and leave to set. Once the chocolate has set your cake is ready to serve and enjoy!