Preheat the oven to 350°F (175°C)
Grease a baking dish
Peel, core, and slice apples
Toss apples with sugar, cinnamon, and lemon juice
Spread the apple mixture evenly in the baking dish
Mix flour, oats, brown sugar, cinnamon, and salt in a bowl
Cut in cold butter until the mixture becomes crumbly
Sprinkle the topping evenly over the apples
Bake for 40 to 50 minutes until the apples are tender and the topping is golden brown
Let cool slightly before serving