Roll the chilled pastry into a 13-inch circle on a sheet of lightly floured wax paper. Invert it over a 9- to 9-1/2-inch deep-dish pie pan and peel off the paper. Tuck the pastry into the pan without stretching; then, sculpt the overhang into an upstanding ridge. Place the pie shell in the freezer while you make the filling. Preheat oven to 375°.
Put the peaches in a large bowl. Stir in sugar, cornstarch, lemon juice, and lemon zest. Set aside while you make the topping.
Put the flour, brown sugar, oats, cinnamon and salt in the bowl of a food processor. Pulse several times, to mix. Remove the lid and scatter the butter over the dry mixture. Process again until the mixture is finely textured but do not over-process. Transfer the mixture to a large bowl and rub between your fingers until you have clumpy crumbs.
Pour the filling into the pie shell and smooth the top. Spread the topping over the filling, tamping lightly to even it out. Bake the pie on the center oven rack for 50 to 55 minutes, until the pie is bubbly and the topping is golden brown. If the top starts to get too brown, cover it loosely with aluminum foil. Transfer to a rack and cool for at least an hour before serving.