01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, allowing overhang for easy removal.
02 - In a large bowl, combine flour, oats, sugar, salt, and cinnamon. 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 extract, beating until fully combined and no lumps remain.
05 - Evenly spread the cream cheese mixture over the pressed crumble base, using an offset spatula for smooth coverage.
06 - Toss diced peaches with cornstarch, lemon juice, and sugar in a bowl until evenly coated. Arrange peach mixture over the cream layer.
07 - Sprinkle reserved crumble mixture evenly over peaches. Bake for 38 to 42 minutes until top is golden brown and center is just set.
08 - Cool completely in pan, then refrigerate at least 2 hours. Use parchment overhang to lift out, slice into 12 bars, and serve chilled or at room temperature.