In a bowl, mix together fruit, lemon juice, zest, sugar, and cornstarch.
Unroll pie crust. Flatten with a rolling pin if necessary to remove any creases. Dough should be 1/8-inch thick, and 10-12 inches in diameter. Place crust on a piece of parchment paper on a large, rimmed baking sheet.
Using a slotted spoon, pile fruit mixture onto the center of the pie crust, spreading out into an even layer, leaving a 2 or 3 inch border from the edge of the crust.
Fold the edges of the dough over the fruit, pleating as you go, and pinching the folds gently to seal them. Place the galette on its baking sheet in the freezer for 15 minutes to chill.
Remove from the freezer. Brush galette with egg wash, and sprinkle with turbinado sugar.
Bake on the center rack in the oven for 35 minutes, or until golden brown and filling is bubbly. Serve warm with vanilla ice cream. Enjoy!