Preheat your oven to 350°F (175°C).
Peel, core, and slice the apples into thin pieces.
In a bowl, toss the sliced apples with lemon juice and cinnamon.
Transfer the apple mixture to a greased baking dish.
In another bowl, combine flour, oats, brown sugar, and salt.
Cut in the softened butter until the mixture resembles coarse crumbs.
Evenly spread the crumble topping over the apples in the baking dish.
Bake in the preheated oven for 35-40 minutes until golden brown.
Remove from the oven and let cool for a few minutes.
Serve warm, optionally with a scoop of vanilla ice cream.