Turn oven onto 180 degrees bake.
Cream butter and sugar until creamy (if using coconut oil make sure it is at a solid state and it will help to make it cream).
Add the vanilla.
Sift in the cocoa, and the other flours.
Add in the flaxseed.
Slowly mix in the flour and mix until combined.
Add in the cornflakes.
Line a baking tray with baking paper and roll the mixture into even sized balls. Flatten with a fork.
Add the icing sugar, melted coconut oil or butter, cocoa and mix well adding in 1 tbsp water at a time until it reaches a desired consistency.
Spread the icing over each cookie and top with a walnut or coconut.