01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, ensuring paper overhangs edges for easy removal.
02 - Combine flour, oats, sugar, salt, and cinnamon in a large bowl. Cut in cold butter using pastry blender or fingertips until mixture resembles coarse crumbs.
03 - Press two-thirds of crumble mixture firmly into bottom of prepared pan to create even base. Reserve remaining one-third for topping.
04 - Beat cream cheese and sugar until smooth. Add egg and vanilla, continuing to beat until fully combined and creamy.
05 - Spread cream cheese mixture evenly over the pressed crumble crust using offset spatula or back of spoon.
06 - Toss diced peaches with cornstarch, lemon juice, and sugar in bowl until peaches are evenly coated.
07 - Arrange peach mixture over cream layer. Sprinkle reserved crumble topping evenly over peaches.
08 - Bake for 38-42 minutes until top is golden brown and center appears set with slight jiggle.
09 - Cool completely to room temperature, then refrigerate at least 2 hours before slicing. Serve chilled or at room temperature.