Preheat oven to 350° F. Line a square (8x8) baking dish with parchment paper.
Add blueberries, lemon zest, water and arrowroot powder into a saucepan. Bring to a boil over medium-high heat. Reduce heat to a simmer and stir constantly for about 3-5 minutes or until mixture has thickened and some of the blueberries have started to pop. Remove from heat and set aside.
Combine oat flour, rolled oats, coconut sugar and sea salt in a medium mixing bowl.
Add coconut oil to the mixture and using your hands or a spoon combine mixture until it forms into a crumble.
Measure out ⅔ cup of the oatmeal crumble mixture for the topping into small bowl and stir in the hemp hearts.
Add remaining oatmeal crumble mixture to the prepared baking dish and evenly press into down using your hands to form the crust.
Pour blueberry filling on top of your crust.
Sprinkle the oatmeal + hemp crumble on top.
Bake for 35-40 minutes until the bars are golden brown on top and the blueberry filling is bubbling and sticking to the edges of the pan. Remove from oven and place on a wire rack to cool completely. Be patient, if you don’t let them cool before removing them from the pan they will fall apart.
Once cool, cut into 12 bars and enjoy right away or chill in the fridge before serving. I personally like the bars chilled, after they've been in the fridge for a bit.