Preheat oven to 350ºF /180ºC. Line an 8x8 inch pan with parchment paper. 

First, prepare the blueberry filling. In a medium sauce pan, combine the blueberries, agave syrup and lemon juice. Cook on medium heat for 5 minutes. With a fork, mash the blueberries and stir often to prevent the jam from sticking to the pan. 

In a small bowl, combine the cornstarch with a splash of water and add the mixture to the blueberries. Cook for 5 more minutes. At that point the blueberry filling is still quite runny. Set aside, it will thicken a bit while you make the crust. 

In a large bowl or the bowl of a stand mixer, mix the flour, rolled oats, baking powder, cinnamon and salt. Then, add the melted butter, agave syrup, and mix until a crumble forms. Use your hands or a pastry blender to incorporate the butter to the flour mixture.

Place ⅔ of the dough into the prepared pan. Use your fingers or the back of a spoon to firmly press the dough to the bottom of the pan, in an even layer. 

Spread the blueberry filling on top of the dough in the pan and sprinkle the remaining oat mixture evenly over the top of blueberries.

Bake for 35 minutes or until crumb topping is lightly browned. I cover the pan with a piece of foil for the first 20 minutes, to prevent the bars from browning too much. 

Remove from the oven and allow to cool completely before slicing. Enjoy!