Preheat your oven to 375°F (190°C).
In a mixing bowl, combine the diced apples, orange juice, lemon zest, granulated sugar, brown sugar, cinnamon, nutmeg, and salt. Mix well and let it sit for 15 minutes to allow the flavors to meld.
In a small bowl, mix the cornstarch with a few tablespoons of water to create a slurry. Stir this into the apple mixture until well combined.
Roll out the pie crust and line a 9-inch pie dish with it. Trim any excess dough hanging over the edges.
Pour the apple-citrus filling into the pie crust, spreading it out evenly.
Place another pie crust or create a lattice pattern over the top to cover the filling fully.
Brush the top crust with a beaten egg for a golden finish (optional).
Bake the pie in the preheated oven for 30-45 minutes or until the crust turns golden brown and the filling starts bubbling.
Remove the pie from the oven and let it cool for at least 30 minutes before serving.