Preheat the oven to 350°F (175°C). In a mixing bowl, combine sliced apples, lemon juice, brown sugar, cinnamon, and nutmeg. Toss to coat the apples evenly.

In another bowl, mix oats, flour, melted butter, brown sugar, and salt until crumbly. Spread the apple mixture in a baking dish and top with the oat mixture.

Bake in the preheated oven for 30 minutes or until the apples are tender and the topping is golden brown.