Mix the oats and sugar together in a large bowl.

Melt the butter.

Add the melted butter to the oats and sugar (and cinnamon, if included) and combine thoroughly.

Spread the oat crumble topping evenly over the dish to be covered e.g. Precooked fruit.

Bake for 20 minutes at 190C / fan 170C / gas 5 until the crumble top is golden and the fruit is bubbling.