Cut the orange in half and juice it but don't throw the halves away. In a small saucepan, combine the juice, orange halves, caster sugar, water and cinnamon. Bring to the boil and boil for 8 minutes. Remove from heat and allow to cool. Discard the orange halves.
To make the cake:
Preheat the oven to 180 degrees C. Lightly grease a 20x30cm baking tin with olive oil.
Take each sheet of filo pastry and roughly tear into shreds. Fill the baking tin with the filo and set aside while you prepare the remaining ingredients.
Cut one orange in half and slice one half into very thin half moons. Set aside. Zest and juice the remaining oranges.
In a bowl, combine the orange juice, zest, eggs, Greek yoghurt, olive oil, 100g sugar and baking powder. Blend on high speed with an electric mixer for two minutes until the mixture is frothy.
Pour the orange-egg mixture over the filo in the baking tin. Stir gently to ensure the mixture is evenly distributed. Decorate the top of the cake with the orange slices.
Bake 45 minutes or until the filling is set and the top golden. As soon as you take the cake out of the oven, pour over the cooled syrup. Set aside for 1 hour so the syrup can soak in. Enjoy!