First make the mousse by beating the avocado, birch sugar, cocoa powder and walnut drink together in a food processor, adjusting the amount of walnut drink to give the desired thickness. Make sure the avocado is nice and ripe.
Make a small cut in the bottom of each mandarin orange and carefully remove the segments (put them to one side to make a juice or energy drink with carrot and celery, for example). Fill the empty mandarin oranges with the chocolate mousse. Leave to cool in the fridge for at least a couple of hours.
Top off each mandarin orange with some chopped nuts and mint leaves. For the final, terrifying touch, draw a scary face on the side of each mandarin orange with marker pen.