Soak gelatin in cold water.
Heat lemon juice, vanilla, and sugar until just below boiling. Melt in gelatin.
Whip cream to soft peaks and fold in Greek yogurt.
Add food coloring if desired.
Fold in the cooled lemon mixture.
Fill each large lemon silicone mold about 2/3 full with mousse.
Gently press in the frozen lemon curd insert, then a pistachio base.
Freeze until completely solid and ready for demolding.