Preheat the oven to 325°F (160°C). Line a 12-cup muffin tin with liners or lightly grease each cup.

In a medium bowl, mix graham cracker crumbs, sugar, and melted butter until it resembles wet sand. Press about 1 tablespoon into the bottom of each muffin cup to form an even crust layer. Bake the crusts for 5 minutes to set, then remove from oven and let cool while you prepare the filling.

In a large bowl, beat the softened cream cheese until smooth and creamy (use a hand mixer or stand mixer). Add sugar and beat until combined. Mix in the egg, vanilla, cinnamon, and flour until the batter is smooth and not overbeaten.

In a small skillet over medium heat, melt 2 tablespoons butter. Add the diced apples, brown sugar, cinnamon, lemon juice, and a pinch of salt. Cook, stirring occasionally, until apples are tender and mixture is syrupy, about 5–7 minutes. Set aside to cool slightly.

Spoon about 1 heaping tablespoon of cheesecake filling over each pre-baked crust, filling the cups roughly 3/4 full. Top each with about 1 tablespoon of the warm apple mixture, leaving space for the streusel.

In a small bowl, combine oats, flour, and brown sugar. Cut in the cold butter with a pastry cutter or two forks until crumbly. Stir in cinnamon. Sprinkle a little streusel over each cupcake.

Bake the minis at 325°F for 16–20 minutes, or until the centers are just set (they may jiggle slightly). Avoid overbaking; the centers should be creamy.

Let the cheesecakes cool to room temperature in the tin for about 30 minutes, then transfer to the refrigerator to chill for at least 2 hours.

Remove the liners and garnish with a drizzle of caramel or powdered sugar if you like. These are best served cold or slightly chilled.