How to Make It
In a large bowl, combine oats, flour, brown sugar, cinnamon, nutmeg, and salt. Stir with a whisk. Add melted butter; stir until combined. Set aside 1 cup of mixture.
Coat a 4- to 5-quart slow cooker with cooking spray. Place peaches, blackberries, and remaining oat mixture in slow cooker; stir to combine. Sprinkle peach mixture evenly with reserved 1 cup oat mixture. Lightly coat top with cooking spray.
Cook on LOW for 3 hours, until fruit is bubbly and top is browned.