01 - Preheat the oven to 350°F. Line a 9x13-inch baking pan with parchment paper, allowing overhang on 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. Add egg and vanilla, beating until fully combined. Spread cream mixture evenly over the crust.
05 - Toss diced peaches with cornstarch, lemon juice, and sugar. Arrange peach mixture evenly over the cream layer.
06 - Sprinkle reserved crumble mixture evenly over peaches. Bake for 38-42 minutes until top is golden and center is just set.
07 - Let cool completely, then refrigerate for at least 2 hours. Slice into bars and serve chilled or at room temperature.