Preheat oven to 375 degrees. Grease a 9 x 13 baking dish with cooking spray. Set aside.
In a large bowl, combine the cut peaches, lemon zest, lemon juice, granulated sugar, and flour. Gently fold in the blueberries, and allow the mixture to sit for 5 minutes.
Using a slotted spoon, scoop the fruit mixture into the prepared baking dish. This controls the extra liquid in the crisp.
In a small bowl, combine all of the topping ingredients (except the butter) with a fork. Crumble in the butter. I like to do this step with my hands--more control over consistency and it won't stick to your hands as much as a tool.
Sprinkle the topping over the fruit mixture (the more the merrier) and bake for 45 minutes until golden brown and bubbling.