Preheat your oven to 325°F (163°C). Line a standard muffin tin with 9 paper cupcake liners.
In a medium bowl, combine graham cracker crumbs, 2 tablespoons sugar, and 1/4 teaspoon cinnamon. Add melted butter and stir with a fork until all crumbs are evenly moistened. Divide mixture among the 9 lined cups and press firmly into the bottom of each. Refrigerate while preparing other components.
For the streusel, whisk together flour, oats, 1/4 cup brown sugar, and 1/2 teaspoon cinnamon in a small bowl. Pour in 3 tablespoons melted butter and stir until coarse crumbs form. Set aside.
Peel and dice apples into small pieces. Toss with lemon juice in a bowl, then add 2 tablespoons brown sugar and 1/2 teaspoon cinnamon. Stir well and set aside.
Beat softened cream cheese in a large bowl with an electric mixer until completely smooth and creamy. Add 1/3 cup sugar, flour, and vanilla extract. Beat until well combined, scraping down the sides as needed.
Add the egg and mix on low speed just until incorporated. Do not overmix.
Spoon cheesecake filling over chilled crusts, filling each liner about two-thirds full. Distribute diced apples evenly over the top of each cheesecake, pressing gently into the filling.
Sprinkle oat streusel generously over the apples and cheesecake filling.
Bake for 28-30 minutes, until the edges are set but the center still has a slight wobble. Do not overbake.
Remove from oven and let cool completely in the pan at room temperature. Transfer to refrigerator and chill for at least 2 hours before serving.
Serve drizzled with caramel sauce and topped with whipped cream if desired.