For the hand pies: Preheat the oven to 400 degrees F.
Cut each pie crust in half through the middle, then in thirds in the other direction, creating 6 pieces (square off the edges to make rectangles or strips).
Place the blueberries, granulated sugar, tapioca, salt and 1 tablespoon of the lemon juice (save the remaining lemon juice for the glaze) in a small saucepan over medium heat. Simmer and stir until the blueberries release their juices and burst, 4 to 5 minutes. Remove from the heat, add the lemon zest and allow the mixture to cool, about 10 minutes.
Dollop 1 tablespoon cooled blueberry filling on each pie piece. Brush the egg wash along the edges and fold the pie crust; crimp with a fork to seal. Brush each pie with the egg wash and sprinkle with demerara sugar.
Bake on a parchment-lined baking sheet until golden, 15 to 20 minutes. Set aside to cool.
For the glaze: Whisk together the confectioners' sugar and 2 tablespoons of the lemon juice, 1 tablespoon at a time, until a pourable glaze forms. Keep at room temperature until ready to use.
When serving, use a spoon to swizzle the top of each hand pie with the lemon glaze.