In a food processor, add walnuts and blend until coarsely ground. Add remaining ingredients for the cake base and pulse until the mixture comes together. Press into a cake tin, and set aside in the refrigerator.
Make the filling:
In a blender, add all smoothie ingredients and blend into a smooth puree. Pour ingredients over the crust and freeze until set, about 2 1/2 hours. Garnish with blueberries and edible flowers.