1. Preheat your oven to 180 degrees celsius and line a square baking tin with parchment paper.
2. Add all of the base ingredients to a bowl and mix until well combined. 
3. Set aside a third of this mixture to sprinkle on top later. 
4. Add your frozen fruit to a pan and cook for 5-10 minutes until the berries have softened and the sauce is thickening. Add in the maple syrup, corn flour and chia seeds and continue to cook this until it starts thickening to a jam. 
5. Press two thirds of the crumble mixture into your lined baking tray and then add the jam mixture on top. Crumble the remaining oat mixture on top and bake for 20 – 25 minutes then cover in foil and cook for another 10 minutes. 
6. Once cooked, leave to cool for 5-10 minutes before slicing and serving.

This recipe is so delicious and will be a hit with friends and family. Slice the crumble into 9 – 12 squares and store in an airtight container for up to two weeks!