Preheat the oven to 350°F.
In a large mixing bowl, combine the blueberries, sliced peaches, lemon juice, granulated sugar, cinnamon, and vanilla extract. Gently toss until the fruit is evenly coated.
Transfer the fruit mixture to a greased 9x13-inch baking dish.
In another bowl, mix together the flour, rolled oats, brown sugar, and salt.
Pour in the melted butter and stir until the mixture is crumbly.
Sprinkle the crumble topping evenly over the fruit mixture in the baking dish.
Bake in the preheated oven for 30-35 minutes, or until the topping is golden brown and the fruit is bubbling.
Allow to cool for at least 10 minutes before serving.