Grease a Swiss roll tin 23cm x 33cm and preheat the oven to Gas 5, 190°C (170c fan), 375°F. Mix the flour and salt and roughly rub in the margarine. Stir the oats and sugar into the mixture and use your hands to combine (it will be a thick doughy mixture).
Press half of the oat mixture into the prepared tin. Sprinkle over the raspberries and strawberries, squashing slightly to release the juice. Cover with the remaining oat mixture then press down firmly. Bake for 25-30 minutes or until golden brown. Leave to cool for 10 minutes then cut into squares.
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