Preheat the oven to 425 degrees F. Line a baking sheet with parchment paper.
Place the chopped strawberries in a bowl. Sprinkle with the sugar, cornstarch, and salt, tossing well. Let sit for 15 to 20 minutes, until the berries have released some juice!
Slice both sheets of puff pastry into 9 squares, like a tic-tac-toe board.
Use a slotted spoon and add about a tablespoon of the strawberries to each square. Fold one corner to meet the other and press the edges together with a fork to seal them.
Whisk together the egg and water and brush it on the pastry triangles.
Place the sheet in the oven and bake the triangles for 20 to 25 minutes, until golden brown.
Let cool for 5 to 10 minutes.
While the turnovers are baking, take 2 to 3 tablespoons of the remaining strawberry juice in the bowl and whisk it with the powdered sugar to create a glaze.
After 5 to 10 minutes, drizzle the turnovers with the strawberry glaze. Sprinkle the chopped pistachios on top. Serve immediately!
