Roll the dough out on a lightly floured surface to make a 12-inch round. Transfer to a large rimmed baking sheet lined with parchment paper.
Combine the strawberries, jam, cornstarch, lemon juice and lemon zest in a medium bowl and gently stir to coat.
Spread the strawberry mixture, including the juices, on the center of the dough, leaving a 2-inch border. Fold the edges over the filling, pleating as needed and leaving the center open. Brush the edges of the dough with the beaten egg and sprinkle with the sugar.
Bake until the crust is golden brown and the filling is tender and bubbling, 25 to 35 minutes.
Transfer to a wire rack to cool to room temperature, about 30 minutes. Slice and serve with a dollop of whipped cream or a scoop of ice cream.