Chop the bananas into 6 pieces each and place in a plastic box or bag in the freezer for 2-4 hours. Break the chocolate into pieces and place in a covered dish in the microwave, on medium-high for 1-2 minutes until melted. Put the frozen bananas into a food processor or blender and blend for 30 seconds. Add the vanilla essence, maple syrup and oatmilk, and blend again for 30 seconds. Finally add the melted chocolate and blend again until well mixed and frothy. Serve in tall glasses.