In a medium bowl add the mascarpone and powdered sugar. Whip with an electric mixer until well incorporated. Add the lemon juice and zest and the vanilla. Mix together until light and fluffy. The filling mixture can be refrigerated for a few hours until ready to use.

Spread the lemon mascarpone onto the bottom of each croissant. Place the sliced strawberries over the mascarpone and let the edges of the strawberries stick out of the croissant. Put the top half of the croissant on top of the strawberries and dust with powdered sugar. Serve immediately.