Preheat oven to 350°F. Line a 9 inch square baking pan with parchment paper.
In a large bowl, stir together oat flour, rolled oats, chia or flaxseed, and salt. Add coconut oil and maple syrup and combine. If it feels too dry, add a couple drops of water. The batter should stick together.
Pour 1 ¾ cup of dough into the prepared baking pan, and press evenly using a back of a spoon or spatula. Set aside.
Filling: In a small saucepan, add the blueberries, tapioca flour or arrowroot starch, maple syrup, lemon juice, lemon zest, cinnamon. Cook for about 3-4 minutes until it starts to thicken. Take a fork and mash some of the blueberries. Pour the blueberry mixture over the crust, and then add the remaining ¾ cup over the blueberry mixture and using a spatula, lightly pat down the topping. Option is to sprinkle chopped nuts.
Bake for 35 minutes or until crispy on top and golden. Remove from oven, place baking pan on a cooling rack. Allow to cool before cutting about 2-3 hours. The longer it sits, the blueberry mixture will set and it will prevent the bar from crumbling.
Store in an airtight container at room temperature for up to 3 days or in the refrigerator for up to a week. They will freeze to 6 months.
