Cake: Preheat the oven to 180 degrees C. Grease two 23cm non-stick springform cake tins. Line bottoms of tins with baking paper.
In a large bowl, sieve together plain flour, caster sugar, cocoa, baking powder and bicarbonate of soda.
Add almond milk, vanilla and vegetable oil. Mix well. Add grated zucchini and mix until all is well combined. Divide the mixture evenly between the two prepared cake tins.
Bake for 25 to 30 minutes until an inserted cake skewer comes out clean. Leave the cakes to cool for 5 minutes in their tins then carefully remove sides of the springform cake tins. Run a palette or rounded knife on the inside edge of the cake tins first to make sure the cake comes out neatly. Cool completely.
Icing: In a bowl, melt the dairy free butter with the boiling water. In a separate bowl, mix together the icing sugar with sieved cocoa powder. Add the melted butter to the sugar mixture. Blend well until you have a smooth icing.
To Assemble: Place one cake on a serving plate and spread some chocolate icing, then top with the other cake.
Ice the cake all over with the chocolate icing with a palette knife. So it does not get too messy you can place some long strips of baking paper around the edges of the cake while you ice it. Leave to icing to set (around 20 minutes).