Preheat the oven to 190°C/375°F/gas 5. Peel and core the apples, quarter and cut in to chunks.
Put the apples in to a pan with the sugar and water. Cook over a low heat for 5 minutes and place in a small oven proof dish.
Place the flour and oats in a bowl and mix well. Cut the margarine or butter in to small cubes and add this to the oats and flour. Mix with your fingertips until it resembles an even crumb texture. Add the sugar and mix through.
Cover the fruit with the crumble mixture. Bake for approximately 20 minutes until the crumble is golden and the apple hot.