Preheat oven to 350 degrees F. Line an 8×8 square baking pan with parchment paper.
In a medium pot over medium heat, add berries and maple syrup. Use a wooden spoon to stir until fruit begins to boil. Add in the cornstarch and stir continuously. Turn heat down and simmer for 3-5 more minutes until thickened. You can use the back of the spoon to smash the berries a bit. Remove pot from heat and set aside while you make the crust/crumble.
In a large bowl, add the oat flour, almond flour, oats, salt, baking soda, and cinnamon. Stir until well combined. Then add the melted coconut oil, maple syrup, and vanilla and stir until well combined.
Place 2/3 of the mixture into the lined pan and place the rest in the fridge. Press dough down firmly into the bottom of the pan.
Pour berry mixture into pan on top of the crust. Take the rest of the crumble mixture out of the fridge. Crumble the remaining dough evenly all over the top of the berry filling.
Bake in the oven for 35-40 minutes, or until top is golden. Allow bars to cool completely in the pan and transfer to the fridge to chill for a few hours. Slice and enjoy! Store leftovers in an airtight container in the fridge for up to 5 days.