Place the diced strawberries and granulated sugar in a saucepan over medium heat.

Stir the strawberries and sugar frequently until the berries have released their juices and softened. Reduce the heat to low and stir in the cornstarch, water, and lemon juice. Cook the strawberry mixture until thickened, constantly stirring, about 10 minutes. Remove the pan from the heat and stir in the vanilla extract. Allow the mixture to cool for at least 30 minutes.

Preheat the oven to 400° F and line a baking sheet with parchment paper. Make the egg wash: Whisk the egg and 1 tablespoon of water in a small bowl.

Roll out each puff pastry sheet on a lightly floured surface and cut each sheet into 4 squares. *There will be eight turnovers in total.

Divide the cooled strawberry mixture (about 2 tablespoon per pastry) between the 8 squares of pastry, diagonally placed on the end of each square. Leave enough room to seal the pastry. Place a small amount of egg wash along the edge of the strawberry filling using your finger or a brush. Fold over the other side of the pastry to form a triangle. Repeat until all of the pastries are filled. Press down the edges of each pastry with a fork. Transfer the turnovers to the prepared baking sheet.

Brush the top of each pastry with egg wash. Bake the turnovers for 18-20 minutes or until the pastry is golden brown and puffed. Allow the pastries to cool while you make the icing.

To make the icing, Whisk the powdered sugar, milk, and vanilla extract until thickened and combined. Drizzle the glaze over each cooled turnover and allow it to set before serving.