Add the lemon or orange zest to the strawberries and carefully stir this through. In a bowl, mix together the mascarpone, cream, vanilla seeds and icing sugar.
Place 6 shortbread rounds on a board and arrange a layer of sliced strawberries on top. Then using a teaspoon divide the mascarpone cream between each one, followed by another layer of strawberries. Finish with another shortbread round and a dusting of icing sugar.