Preheat the oven to 400°F. Line the baking sheet with parchment paper to prevent the puff pastry from sticking to the pan.
Open the defrosted puff pastry dough. Cut each puff pastry piece into 4 rectangles.
Place pieces on parchment paper on the baking sheet.
Using a knife, cut a shallow score (cut) about ½” all the way around the outside of each pastry piece.
In a small bowl, whisk together egg and water. Brush the edges with egg wash.
Poke the pastry (except the edges) with a fork 3-4 times.
Spread 2-3 tablespoons of blueberry pie filling inside the scored edges.
In a medium bowl, mix topping ingredients together with 2 forks or a pastry blender.
Sprinkle some topping over the blueberry filling.
Bake for 20 minutes or until puff pastry is puffed up and the topping is golden.
While the pastries are cooling down, mix powdered sugar and water in a small bowl. Use a fork or piping bag to drizzle the glaze over the pastries. Serve.