Preheat oven to 350 degrees.
Combine all cookie base ingredients either by hand or in a food processor until coarse crumbs form. It will look like moist sand and not look like it will hold together at this point.
Line an 8"x8" pan with parchment (allowing for some overhang which will make removing easier) and lightly spray with cooking spray.
Firmly press the cookie base into the bottom of the pan making sure it is even, center to edges. Use the bottom of a glass if necessary.
Bake for 20-30 minutes until golden and fully set. It seems slightly soft when you first remove it but crisps up nicely as it cools. Allow to cool completely.
In a small bowl, combine the cream cheese and powdered sugar. Set aside at room temperature.
In a small bowl, crush 1/2 of the peaches.
In a small saucepan over medium heat. Add sugar and cornstarch. Stir in the crushed peaches and water. Stir constantly until mixture boils and thickens. Set aside to cool for 10 minutes.
Gently fold in the remaining peaches and the blueberries.
On the now cooled cookie base, evenly spread the cream cheese filling.
Top with the peach and blueberry mixture and refrigerate for 1 hour or until set.
Store covered in refrigerator.