Preheat the oven to 180 degrees Celsius.
Spray a baking dish with 1kcal spray.
Add in the apples and spread out evenly.
In a bowl, mix the caster sugar, demerara sugar, lemon juice, flour, oats, butter, cinnamon and salt to make the crumble topping.
Sprinkle the topping over the apples.
Spray again with 1 kcal spray.
Bake for 30 minutes until golden brown.
Serve hot with some low calorie vanilla ice-cream/custard.