Preheat to 350°F (175°C). Lightly grease a 9x13-inch baking dish.

In a large bowl, toss sliced apples with lemon juice, sugars, cinnamon, nutmeg, and flour until evenly coated. Pour into prepared baking dish and spread evenly.

In another bowl, combine oats, flour, brown sugar, granulated sugar, cinnamon, and salt. Cut in cold butter using a pastry cutter or fork until the mixture is crumbly and holds together when pressed.

Evenly distribute the topping over the apples. Press down slightly to ensure the topping sticks. Bake uncovered for 40–50 minutes, or until the topping is golden brown and the apples are bubbling at the edges.

Let the crisp cool for 10–15 minutes before serving. Delicious on its own or topped with vanilla ice cream or whipped cream.