Preheat the oven to 180C (355F). Grease a baking dish (I used a 28cm square, 7 cm deep dish) and set aside.
Peel, core and cut all the apples into thin wedges. Place the apples into the baking dish.
Put the white sugar, flour, and cinnamon into a bowl and mix it with a fork. Sprinkle the sugar mixture over the apples and coat all the apples evenly. Pour in the water and lemon juice over the apples and coat all the apples evenly.
Place all the topping ingredients into a big bowl. Mix with a fork until well combined. Sprinkle the crumble over the prepared apples. Bake for around 35 minutes or until the crumble turns a nice golden brown.
Serve warm with some vanilla ice-cream. Store covered in the fridge for up to 5 days. Heat in the microwave or oven before serving again.
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.