Preheat the oven to 350°F.
Place the diced peaches in an oven-safe pie plate and set aside.
In a medium bowl, mix together the melted butter, brown sugar, flour, cinnamon, and rolled oats until crumbly.
Place crumbly mixture on top of peaches and press down, covering all of the peaches.
Bake for 40-45 minutes.
Let cool at least 10 minutes before serving.