Take out a 8″x 8″ or 9″x 9″ square glass baking dish and preheat your oven to 200°C/400°F/gas mark 6.
For the fruit base
In large bowl toss together the fruit base ingredients. Scoop into the baking dish and pat down. This is to keep the fruit juicy while baking and also to allow room for crumble topping.
For the crumble topping
In a high speed blender or food processor, grind ½ cup of oats into flour. Using the same large bowl (no need to clean), put the ground oat flour, oats, walnuts, maple syrup and cinnamon into bowl and toss together. Spread crumble topping onto the fruit base trying to completely cover the fruit. Pat the topping down, this will help prevent the crumble from burning.
Bake in oven for 40-45 minutes.
Let cool for 30 minutes before serving.
Store in fridge covered for up to 1 week.
If you don’t have a juicer, replace with 3½ cups thinly sliced apples. Pears work well in place of apples as do other berries in place of blueberries.