Preheat oven to 375°F.
If using frozen peaches, remove from freezer and let thaw for approximately 30 minutes.
Remove pie shell from freezer and place on a cookie sheet.
If using fresh peaches, peel, pit and slice.
Place cold stick of butter into medium size bowl and slice into 1/4″ slices.
In separate bowl, mix together sugar, flour, salt and cinnamon.
Add sugar, flour, salt and cinnamon to butter and fork together until crumbly.
Sprinkle 1/4 cup of the dry mixture on the bottom of the pie shell.
Add peaches to the pie shell.
Add pecans and oat flakes to the remaining dry mixture and combine.
Pour dry mixture over peaches.
Tent aluminum foil over pie, place in oven and bake for 45 minutes.
Remove foil tent and bake for an additional 5 minutes or until peaches are tender and topping is golden brown.
Serve warm or once cooled. Can be served for up to 3 days.