Preheat the oven to 180°C. Grease two medium sized heart-shaped silicone cake moulds.
Combine all the ingredients for the sponge in a mixing bowl and beat with an electric hand-held whisk for 1-2 minutes until smooth. Spoon into the moulds and level off. Bake for 12-15 minutes until golden and risen. Remove from the oven and allow to cool in the moulds to one side.
Meanwhile, purée the strawberries for the topping in a food processor. Strain through a sieve into a clean bowl. Beat together the softened butter and icing sugar in a separate mixing bowl until soft. Add the purée, mix well again until evenly combined and set to one side. When you are ready to assemble to cake, turn the cakes out of their moulds.
Spread some of the Greek yogurt onto the base of one of the sponges, then arrange the strawberries for the filling on top. Spoon the rest of the Greek yogurt on top. Spread the top of the other sponge cake with the topping mixture, using a warm, wet palette knife to ensure an even finish.
Sprinkle some of the sesame seeds on top.
Sandwich it on top of the base layer of the cake and transfer to a serving plate. Garnish the top with the slices of the strawberry and the julienned lemon zest before serving.