In a large mixing bowl, beat the egg whites until foamy. Add cream of tartar and vanilla; beat until soft peaks form. Gradually beat in sugar, 1 tablespoon at a time, until stiff glossy peaks form. Fold in saltines and pecans.
Transfer to a 13"x9"x2" baking dish coated with nonstick cooking spray. Bake at 350 degrees for 20-25 minutes or until lightly browned and edges begin to crack. Cool on a wire rack. Spread whipped topping over crust. Carefully spoon pie filling over top.