Use a 6-quart slow cooker. Pour the water into the bottom of the slow cooker insert. Place the peach halves, skin-side down, into the water. Evenly spoon the granola into the peach halves and top each with a pat of butter.

Cover and cook on low for 4-5 hours or on high for about 2 hours. Your peaches are finished when the skin begins to pucker and the peach flesh has darkened and can easily be cut with a spoon. Unplug the slow cooker and let your dessert sit in it for about 15 minutes before removing. Serve with whipped cream or ice cream, if using.