Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper.
In a bowl, combine graham cracker crumbs, melted butter, sugar, and cinnamon.
Press the mixture firmly into the bottom of the prepared pan.
Bake for 10 minutes, then allow to cool while preparing the other layers.
In a mixing bowl, beat cream cheese and sugar together until smooth.
Add eggs one at a time, mixing thoroughly after each addition.
Stir in the vanilla extract until well combined.
Pour the cream cheese mixture over the cooled crust and spread it evenly.
Toss the diced apples with lemon juice, brown sugar, cinnamon, and nutmeg in a separate bowl.
Evenly distribute the apple mixture over the cheesecake layer.
In another bowl, mix together flour and brown sugar.
Cut in the cold butter until the mixture becomes crumbly.
If using, stir in the chopped pecans until well incorporated.
Sprinkle the streusel topping over the apple layer evenly.
Place the pan in the preheated oven and bake for 45-50 minutes, or until the streusel is golden and the cheesecake is set.
Allow the dessert to cool completely at room temperature, then refrigerate for at least 2 hours.
In a saucepan, combine sugar and water. Heat over medium heat, stirring until the sugar is fully dissolved.
Increase the heat to medium-high and cook without stirring until the mixture turns amber (approximately 8-10 minutes).
Remove the saucepan from heat and carefully whisk in the cream (the mixture will bubble vigorously).
Stir in the butter and salt until the mixture is smooth.
Let the caramel sauce cool slightly.
Cut the chilled bars into squares.
Drizzle the warm caramel sauce over the bars just before serving.
