Preheat oven to 180°C.
Lightly grease a 16x26cm baking pan and line with baking paper. Break up biscuits. Place into a mixing bowl with coconut and Akta-Vite. Sift over flour and stir.
Melt butter in a small saucepan over a low heat. Pour over dry ingredients. Add vanilla. Mix well.
Spoon mixture into prepared pan and press down to level. Bake for 15 minutes or until cooked.
Sift icing sugar and cocoa into a small bowl. Add water and stir well. Ice slice while still hot. Cut into squares to serve.