01 - Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper 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. Add egg and vanilla, beating until fully combined and creamy.
05 - Spread the cream cheese mixture evenly over the pressed crumb crust.
06 - Toss diced peaches with cornstarch, lemon juice, and sugar in a bowl until well coated.
07 - Arrange the seasoned peach mixture evenly over the cream cheese layer.
08 - Sprinkle the reserved crumble mixture evenly over the peaches.
09 - Bake for 38 to 42 minutes until the top is golden brown and the center is just set.
10 - Let cool completely to room temperature, then refrigerate for at least 2 hours before slicing into bars. Serve chilled or at room temperature.