Set the oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.
Mix graham cracker crumbs, sugar, and melted butter until it looks like wet sand. Add 1 tablespoon to each liner, press flat, and bake for 5–7 minutes. Let cool.
Beat cream cheese and sugar until smooth. Mix in vanilla and egg, then fold in sour cream. Spoon the batter into each liner, filling about ¾ full.
Toss diced peaches with brown sugar, cinnamon, nutmeg, melted butter, flour, and oats (if using). The mix should be sticky. Add 1 tablespoon on top of each cheesecake.
Bake for 20–25 minutes until the cheesecakes are set and the topping is golden and slightly bubbly. The centers should jiggle slightly.
Cool in the pan for 30 minutes, then refrigerate for at least 2 hours.
Top with whipped cream and a pinch of cinnamon. Serve chilled.