In a large bowl, add the peaches, sugar, lemon zest and juice, vanilla, flour and nutmeg. Toss lightly to evenly coat. Fold in blueberries and pour mixture into prepared pan. Let sit while you prepare the crumble topping.
In a large bowl, combine the flour, oats, sugar, cinnamon and salt. Use a pastry cutter or your fingers to cut in butter until mixture forms coarse crumbs. Sprinkle the topping evenly over the fruit mixture and bake for 45-50 minutes, until the topping is browned and set and the juices are bubbly. Transfer to a wire rack and let cool for 10 minutes. Serve warm (or room temperature) with vanilla ice cream on top. Enjoy!