Mix oats with flour, sugar, cinnamon and margarine until it is a crumble consistency.
Grease a baking tray (20x20cm) or line with a silicone liner.
Spread a thick layer (1.5cm) on the base of the tray.
Cover with layer of frozen berries (no need to defrost).
Top with a thinner layer of the crumble mix and press down with a fork.
Sprinkle with the linseeds.
Bake at 180C/Gas mark 4 for 45 mins.