Preheat your oven to 350°F (175°C) and line a muffin tin with cupcake liners.

In a mixing bowl, combine graham cracker crumbs, melted butter, and sugar until well blended. Press this mixture into the bottom of each liner to form a crust. Bake for about 5 minutes until lightly golden, then remove and set aside.

In another bowl, beat the softened cream cheese until smooth. Add sugar, egg, and vanilla extract, mixing until velvety. Spoon the cheesecake filling over the cooled crusts, filling each cup generously.

Melt a tablespoon of butter in a skillet over medium heat and sauté diced apples with sugar and cinnamon for 3-4 minutes until tender. Allow to cool slightly, then add a spoonful to each cheesecake.

Combine oats, all-purpose flour, brown sugar, melted butter, and a pinch of salt in a bowl. Mix until crumbly, then sprinkle over the apple layer on each cheesecake.

Bake for 18-20 minutes, until centers jiggle slightly but are set. Cool in the muffin tin for 15 minutes before transferring to a wire rack.

Once cooled, cover with plastic wrap and refrigerate for at least 2 hours. Remove liners and serve on a platter.