Mash the avocado in a bowl. Add the remaining ingredients, except for the dark chocolate, and stir well.

Add a drop of cold water and mix well to form a thick paste.

Transfer to a tray lined with baking paper. Spread out evenly with a spatula. Refrigerate for 2 hours (or freeze for around 1 hour) until firm. Cut into 9 pieces. Serve.

Store any leftovers in an airtight container and freeze on same day. Thaw for 10 minutes before serving.