Wipe the apples and cut them into quarters, then remove the cores and slice each piece in two. Put them into a pan, taste a slice for sweetness and add a sprinkling of sugar accordingly. Add a tablespoon of water or apple juice and cook over a medium heat for about five minutes, until the apples start to soften.
Transfer the apple mixture to a shallow ovenproof pie dish.
Blend the flour and butter in a food processor for a few seconds, until the mixture looks like breadcrumbs.
Stir in the oats and the brown sugar and sprinkle over the cooked apples in the pie dish. Transfer to the oven to bake for 30 minutes or until crisp and golden-brown on top.