Preheat the oven to 180°C, fan 160°C, gas mark 4. Grease and line an 18 x 28cm baking tin with baking paper.
Tip the apple into a saucepan with 6 tablespoons of water, cover with a lid and cook until soft (about 5-6 minutes). Drain the excess water and puree in a blender or mash with a potato masher.
Tip 200g of the oats and the cinnamon (if using) into a large bowl and add the cooked apple and two-thirds of the caramel. Mix well.
For the base: spread two-thirds of the oat mixture onto the base of the tin and push into the corners with the back of a spoon for a completely smooth layer.
Tumble the berries on top of the base. Beat the remaining caramel in the can then drizzle over the berries.
Make a crumbly topping: add the last 55g of oats to the remaining mixture in the bowl and mix well. Using your fingers rub in the butter (it gets a little messy!). Add the almonds and stir together.
Dot the final oat mixture over the berries and press down slightly to stick all the layers together. Bake for 25-30 minutes until golden brown.
Leave to cool completely before cutting into squares. Enjoy with a blob of Greek yogurt or clotted cream.