Mix water and caster sugar in a small saucepan and cook over medium heat for 5 minutes until slightly thickened.
Cream
Whisk cream, icing sugar and cinnamon together until soft peaks are formed. Gently fold in Greek yogurt.
Assembling
Slice sponge into 2cm cubes and arrange half at the bottom of the trifle bowl. Pour half the sugar syrup over the chopped sponge. Top with half the berries and spread half the cream on top.
With the remaining sponge create another sponge layer and pour the remaining sugar syrup. Ice with the remaining cream and decorate with berries.
Dust with icing sugar to finish.