Preheat the oven to 350°F and place the pie crust in a 9-inch deep-dish pie pan. Decorate or crimp the crust, as desired, and place in the refrigerator while you make the filling.

In a large bowl, combine the sliced apples, orange zest, lemon zest, lemon juice, brown sugar, cinnamon, nutmeg, and cornstarch. Mix well and set aside while you make the crumb topping.

To make the topping, add the flour, xanthan gum, sugars, salt, and oats to the bowl of a stand mixer fitted with the paddle attachment. Mix to combine.

Add the cubed butter and mix on low to incorporate until the dough starts to come together.

Transfer the apples to the pie crust, spreading them evenly in the crust. Crumble the topping over the apples.

Place the baking dish over a rimmed baking sheet (in case the apples bubble over) and bake for 45-60 minutes or until the topping is browned/crisp and the apples are bubbling. Use a pie shield or piece of foil placed around the edges to prevent your crust from burning, if necessary.

Cool the pie at least 2-3 hours before serving. Serve warm with vanilla ice cream or homemade whipped cream.