In a large bowl, combine blueberries, sliced peaches, lemon juice, lemon zest, vanilla extract, granulated sugar and flour. Gently toss until fruit is well coated. Allow the fruit mixture sit while you prepare the crumble topping.
For the crumble topping, take a large bowl and combine the flour, oatmeal, brown sugar, granulated sugar, salt, and cinnamon. Stir together with a whisk. Mix in the butter with your hands until its forms a coarse mixture and there are big crumbles.
Place the fruit mixture in a glass baking dish. Sprinkle the crumble mixture evenly over the fruit. Bake for 40 to 45 minutes, or until the top is browned and crisp and the juices are bubbling. Serve warm with vanilla ice cream.
Store crisp covered in the refrigerator for up to 3 days.24-hour make ahead tip: Prepare the filling, cover and store in the refrigerator. Make the crisp topping and store in a separate container in the refrigerator. Assemble crisp and bake according to instructions.Freezing instructions: Bake and cool crisp completely. Cover tightly with a double layer of aluminum foil. Freeze for up to 1 month. Defrost overnight in the refrigerator. Reheating instructions: Preheat oven to 350 F. Bake for 20 minutes or until heated through.