Core and dice 500 grams (3-4) apples and place them, along with 60 grams (1/4 cup) dates and 1 tablespoon water, into a small saucepan.
Cook on medium heat for 5-10 minutes, or until soft. Stir in the cinnamon and cool slightly before blending until smooth. I use an immersion blender, but a heat-safe standing mixer would also work.
Set aside to cool while you make the base mixture.
Base and Crumble Topping
Preheat your oven to 180C (350F) and line a 20cm (8-in.) square baking tin with parchment paper.
In your food processor, grind 250 grams (2 cups) oats into flour.
Mix on high speed until a slightly crumbly dough forms. You should be able to press it between your fingers have it hold its shape. If it's too dry, add 1 tablespoon milk and mix again.
Using your hands, press about two-thirds of the dough into the prepared baking tin and reserve the rest for the crumble topping. Try to make it as even as possible, as it will be quite thin.
Spread the apple filling over the base and then top with the remaining crumble mixture.
Bake for 18-22 minutes, or until golden. Remove from the oven and cool completely in the tin before removing and slicing.
Store the bars in a sealed container in the refrigerator for up to five days, or freeze for up to a month.