For crust, line the unbaked pastry shell with a double thickness of foil. Bake in a 450 degree F. oven for 8 minutes. Remove foil. Bake for 4 minutes more. Remove from oven. Reduce oven temperature to 350 degrees F.
For filling, peel, core, and slice apples. In a medium mixing bowl stir together eggs, applesauce, yogurt, granulated sugar, 1/2 cup brown sugar, oats, and cinnamon. Stir in bread and apples. Set aside.
For topping, in another mixing bowl stir together 1/4 cup packed brown sugar and flour. Cut in butter until mixture resembles coarse crumbs. Stir in nuts. Pour filling into the prepared pie crust. Sprinkle topping over filling. Cover edge of crust with foil. Bake for 30 minutes. Remove foil; bake 30 minutes more or until top is golden and fruit is tender.