Preheat the oven to 350 degrees F.
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. Let the fruit mixture sit while you prepare the crumble topping.
For the crumble topping: in a large bowl, combine the flour, oatmeal, brown sugar, granulated sugar, salt, and cinnamon. Stir together with a whisk. Mix in the butter with your fingers until the mixture comes together and you have big crumbles.
Place the fruit mixture in a 2-quart ceramic, glass baking dish, or large cast iron skillet. Sprinkle the crumble mixture evenly over the fruit.
Place the pan on a large baking sheet and bake for 40 to 45 minutes, or until the tops are browned and crisp and the juices are bubbly. Serve warm or at room temperature. We like to serve our crumble with vanilla ice cream.