Preheat oven to 350° F. Prepare a 9x13 baking dish by spraying evenly with baking spray or spreading a thin layer of softened butter evenly over the bottom and up the sides.
In a large bowl, combine peaches, cinnamon, 1/4 cup brown sugar, and cornstarch.
In medium-sized bowl, add oats, pistachios, 1/2 cup brown sugar, flour, and butter. Using a pastry blender or fingers, combine until butter is incorporated and ingredients are evenly crumbled together.
Pour peach mixture into baking dish. Sprinkle oat mixture evenly over top of peaches. Place in oven and bake for 30 minutes or until golden brown and bubbly. Allow to rest for 5 minutes until serving. Pour caramel sauce over individual portions if desired.