Serve this apple crisp warm with a scoop of vanilla ice cream on top. This recipe is even better made one day ahead giving the juices and flavors time to meld together.
Heat oven to 350 degrees F. Butter a 9-inch square baking dish. Add apples to a large bowl with orange zest, orange juice, sugar, cinnamon, and nutmeg. Mix until combined and pour into the prepared baking dish.
In a large bowl, combine the flour, oats, sugar, salt, and butter in a medium bowl. Stir until the flour is moist and the texture is crumbly. Sprinkle over the apple filling.
Bake for 1 hour or until the juices are bubbling and the top is golden brown. Place foil on top if the top gets too brown an the apples are not tender enough.