Pulse pecans with brown sugar in a food processor until finely ground (do not allow to become a paste). Add flour, butter, cinnamon, ginger, and salt and pulse until mixture begins to form large lumps. Divide mixture between tart pans and press evenly over bottom and up sides with floured fingers. Chill until firm, about 30 minutes.
Bake tart shells in lower third of oven until golden brown, about 25 minutes. Transfer shells in pans to racks to cool completely. Carefully remove sides of pans, keeping shells on pan base.
Make filling while shells cool: Simmer Port and jelly, stirring occasionally, until reduced to about 1 1/2 cups, about 30 minutes, then stir in lemon juice. Immediately toss grapes with 1 cup glaze in a large bowl until well coated, then mound in tart shells.
Just before serving, drizzle tarts with more glaze and serve remainder on the side.
Cooks' notes: Tart shells can be made 2 days ahead and kept in pans, loosely covered, at room temperature. Remove sides of tart pans before filling.
Port glaze can be made 2 days ahead and chilled, covered. Reheat before proceeding.