Grease a 16x26cm baking pan and line with baking paper. Break up the wholewheat buscuits into a large mixing bowl with the coconut and sugar. Into the same bowl sift in the cocoa and self-raising flour and stir.
Melt the butter and pour of the dry ingredients, add vanilla essence and stir till well combined. (I usually add the essence to the melted butter first).
Spoon mixture into prepared pan and press down to level. Bake for 15 minutes or until cooked.
Icing: Sift icing sugar and cocoa into a small mixing bowl. Add the hot water and stir well. Ice slice while it is still warm.