Preheat your oven to 350°F (175°C).
Peel and slice the apples, placing them in a large mixing bowl.
Add lemon juice, 1/4 cup of brown sugar, and a pinch of salt to the apples. Toss to combine.
Transfer the apple mixture to a greased 9x13 inch baking dish.
In another bowl, combine oats, flour, remaining brown sugar, cinnamon, and nutmeg.
Pour melted butter into the oat mixture and stir until crumbly.
Spread the oat topping evenly over the apple mixture.
Bake in the preheated oven for about 40 minutes, or until the apples are tender and the topping is golden brown.
Allow to cool slightly before serving.
Serve warm with a scoop of vanilla ice cream.