Preheat oven to 350°F (180°C). Line an 8-inch x 8-inch baking pan with parchment paper. Set aside.
In a large mixing bowl, combine all the crust ingredients: oat flour, rolled oats, maple syrup, melted coconut oil, salt, and vanilla.
Squeeze the batter with your hands to bring all the ingredients in contact and create a dough that sticks together. If too dry (may happen if you are using a coarse oat flour), add 1-2 tablespoons of water, add 1 at a time, until the dough is soft and stick together.
Press 1 3/4 cup of the dough all over the baking dish, using a spatula to smoothen the dough and making sure there is no hole left. Set aside leftover dough in a small mixing bowl in the fridge. You will use it for the crumble on top of the bar.
Place the pan in the fridge while you make the blueberry chia seed jam.
Blueberry chia seed jam
In a small saucepan, add the blueberries, maple syrup, lemon juice, lemon zest, and chia seeds.
Cook for 1-2 minutes on medium heat until bubbles form on the sides of the pan.
Mash the blueberries using a fork or potato masher and keep cooking for 2 minutes, stirring all the time to prevent the jam from burning. It should slightly thicken but still be very runny. It will thicken in the oven, don't worry.
Pour the jam on top of the prepared crust then use the remaining dough to crumble all other the bar.
Bake the bar for 35 minutes or until crispy on top and golden.
Remove from the oven and cool in the pan 10 minutes before transferring onto a cooling rack.
Cool for 3 hours or until it reaches room temperature before slicing into 16 bars. Waiting will prevent the bar from crumbling, and the jam will set perfectly.
Store the bars in the pantry in an airtight container for up to 3 days or in the fridge for up to 1 week. Otherwise, freeze and defrost the day before breakfast.
Maple syrup can be replaced with brown rice syrup or agave or coconut nectar.Chia seeds can be replaced with 2 tablespoons of flaxseed meal.Blueberries or any other berries like raspberries, blackberries, or strawberries.