1. Preheat oven to 180C.
2. Chop apples into small cubes.
3. In a sauce pan, add the chopped apples, lemon juice, sugar, cook over low-medium heat for 3 minutes or until apple is slight softened.
4. Combine the flour, sugar, and oats in a bowl. Rub the butter into the flour using fingertips and mix until the mixture resembles breadcrumbs.
5. Transfer apples into an oven-safe dish, sprinkle crumble mixture over the apples, and bake in oven for 20-25 minutes or until golden.
6. Serve warm with ice cream or whipped cream.