01 - Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper, ensuring overhang on all sides for easy removal.
02 - Combine flour, oats, sugar, salt, and cinnamon in a large bowl. Cut in cold butter using a pastry blender or fingertips until mixture resembles coarse crumbs.
03 - Press two-thirds of the crumble mixture firmly into the bottom of the prepared pan to create an even base. Reserve remaining one-third for topping.
04 - Beat cream cheese and sugar until smooth and creamy. Add egg and vanilla, mixing until fully combined and no lumps remain.
05 - Evenly spread the cream cheese mixture over the prepared crust using an offset spatula or back of a spoon.
06 - Toss diced peaches with cornstarch, lemon juice, and sugar until well coated. Arrange peach mixture evenly over the cream layer.
07 - Sprinkle reserved crumble mixture evenly over peaches. Bake for 38-42 minutes until top is golden brown and center is set.
08 - Cool completely to room temperature, then refrigerate for at least 2 hours. Lift from pan using parchment paper and slice into 12 bars. Serve chilled or at room temperature.