Take advantage of another fruit in peak season: Substitute unpeeled nectarines for the plums.
Preheat oven to 425°F. Lightly coat baking sheet with cooking spray.
Make crust: In medium bowl, mix flour, sugar and salt. Using fork, slowly stir oil into flour until mixture is crumbly. Stir in enough ice water so dough will hold together. Press dough into flattened disk.
Roll dough between sheets of wax paper into rough circle, 14 to 15 inches in diameter and approximately 1⁄16 inch thick, patching where necessary. Remove top sheet and invert dough onto prepared baking sheet. Cover and refrigerate while preparing filling.
Spread nuts in pie pan and toast in oven until lightly golden, about 5 minutes. Let cool.
Meanwhile, quarter plums, discarding pits. In food processor, combine walnuts, flour and 1⁄4 cup sugar. Process until finely ground.
Spread flour-nut mixture over pastry, leaving 11⁄2-inch border around edge. Arrange plums, resting on their sides, in concentric circles, over nut mixture. Sprinkle with remaining 1⁄4 cup sugar. Fold pastry border over plums.
Bake 15 minutes. Reduce oven temperature to 375°F and bake until crust is golden and juices are bubbling, 30 to 40 minutes.
Using long spatula, loosen warm tart from baking sheet and slide onto serving platter. Let cool.
Heat jelly in small saucepan over low heat until melted, then brush sauce over plums before serving.