01 - Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper.
02 - Combine flour, oats, sugar, salt, and cinnamon in a large bowl. Cut in the cold butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs.
03 - Press two-thirds of the crumble mixture firmly into the bottom of the prepared pan to form an even base. Reserve the remaining one-third for the topping.
04 - In a separate bowl, beat cream cheese and sugar until smooth. Add egg and vanilla, and beat until fully combined. Spread the cream mixture evenly over the crust.
05 - In another bowl, toss diced peaches with cornstarch, lemon juice, and sugar. Arrange the peach mixture over the cream layer.
06 - Sprinkle the reserved crumble mixture evenly on top. Bake for 38-42 minutes, or until the top is golden and the center is just set.
07 - Allow to cool completely, then refrigerate for at least 2 hours. Slice into bars and serve chilled or at room temperature.