Heat oven to 375ºF (190ºC) with rack set in lower-third. Unroll pie crust and place on a parchment-line baking sheet.
Toss rhubarb with ½ cup sugar, 3 tablespoons minced candied ginger, 2 tablespoons jam, 1 tablespoon cornstarch, grated zest of 1 orange and a pinch of salt.
Layer rhubarb over dough in a spiral working from outside towards center, leaving a 2-inch border around edge of dough. Dollop any remaining ginger-sugar mixture from bowl over top.
Fold outer 2 inches of dough over filling, pleating dough every 2–3 inches as needed. Gently pinch pleated dough to secure, making sure not to pinch dough into fruit. Dollop remaining 2 tablespoons jam over rhubarb.
In a small bowl, beat egg with a splash of water. Brush edges of dough with beaten egg then sprinkle with pistachios and turbinado sugar.
Bake galette until golden brown and rhubarb is tender, 55–60 minutes. Rotating sheet halfway through baking.
Let galette cool on sheet for 10 minutes. Slide onto a wire rack and cool until juices have thickened, about 20 minutes. Serve with whipped cream or ice cream.