Preheat the oven to 350 degrees F. Line an 8×8 pan (or 9×9 for slightly thinner bars) with parchment paper. To make the crust, put the oats in a food processor. Process the oats until a fine flour forms. Add the rest of the ingredients and pulse until it is crumbly, like wet sand. Press firmly into the pan and use the bottom of a large glass to firmly pack it in evenly. Bake for 20-25 minutes until golden. Set aside to cool for a little bit.
While the crust is baking. Make the filling. Add all filling ingredients except for the cornstarch into a medium pot on medium high heat. Simmer and stir for 5 minutes until slightly softened. Turn down the heat to medium low and add in the cornstarch. Stir to combine and until it thickens. Turn off heat and set aside to cool for about 10 minutes.
Make crumble by adding the coconut sugar, 1/4 cup of oats, and cinnamon to the food processor. Process until fine crumbs form. Add the coconut oil. Pulse until it’s combined. Take the blade out and stir in the other 1/4 cup of oats with a fork or your fingers until a crumble forms. Set aside.
After the crust has cooled for 10-15 minutes, add the filling and spread it into an even layer. Then sprinkle with crumble topping evenly across the top. Bake for 30-35 minutes until the top is golden. Let it cool completely before taking it out of the pan and cutting. Enjoy!