Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the sliced apples, lemon zest, lemon juice, granulated sugar, cinnamon, nutmeg, and salt. Toss until the apples are evenly coated and transfer the mixture to the baking dish.
In another bowl, mix the oats, flour, and brown sugar. Add the cold, cubed butter and use a pastry cutter or fork to combine until the mixture resembles coarse crumbs.
In the baking dish spread the oat mixture evenly over the apples.
Bake for 45 to 50 minutes, or until the topping has turned a rich, golden brown, and the apples have become tender.
Before serving let the apple crisp to cool.