Preheat the oven to 350°F.

In a large bowl, combine all the crust ingredients. Mix until well incorporated. It should be slightly crumbly.

In a parchment lined 8 x 8 or 9 x 5 baking dish, press down ⅔ of the oat mixture to create the crust. Reserve the rest for the crumble.

Bake the crust for 10 minutes while you prep the filling. Once done, remove from oven and set aside until filling mixture is ready.

In a medium saucepan, pour in the blueberries over medium heat. Bring to a boil, stirring every few minutes.

Once the berries start to bubble, lower the heat and mix in the lemon juice and maple syrup.

Using a spatula or wooden spoon, gently mash the berries. You can leave some berries whole or in pieces if desired.

Let simmer for 10-15 minutes, stirring occasionally.

Add the vanilla extract and tapioca flour to the blueberries, starting with a tsp at a time. Let the mixture simmer for another 5 minutes until thick.

Pour the filling on top of the baked crust. Crumble the rest of the oat mixture over the filling.

Bake for an additional 20-25 minutes, until the crumble is golden.

Let cool for 10 minutes before slicing into bars.

Keep stored in refrigerator for up to two weeks.