Preheat the oven to 400 degrees F.
In a large bowl, combine the apples, cherries, walnuts, granulated sugar, orange juice, orange zest, 1/4 teaspoon of cinnamon, 1/8 teaspoon of nutmeg and cornstarch and toss well to combine.
In a separate bowl, combine the oats, brown sugar, flour, remaining 1/4 teaspoon of cinnamon, and remaining 1/8 teaspoon of nutmeg. Blend the butter into the dry ingredients using your fingers until the mixture resembles coarse crumbs.
Line a 9 or 10-inch deep baking dish with pie crust and pour in the fruit mixture. Sprinkle the crumb mixture over the top and bake for 20 minutes. Lower the temperature to 350 degrees F and continue baking until bubbly, apples are tender, the top is golden brown, and the pie crust is browned, 35 to 40 minutes longer. Remove from the oven and let rest at least 15 minutes. Serve warm, with vanilla ice cream on top.