Preheat the oven to 350F degrees. 

Zest one lemon and add the zest to a medium-sized bowl. Add in the sugar and using your fingers, rub the zest into the sugar. This helps distribute the oils from the zest into the sugar and distribute the lemon flavor throughout the rest of the ingredients.

Then add in the remaining ingredients for the crisp- brown sugar, flour, oats, salt, and melted butter. Mix to thoroughly combine. 

Next, add the lemon zest and sugar to a bowl and rub together. Then, add the remaining ingredients for the blueberry filling into a medium bowl and toss it to coat it evenly. 

Line an 8x8 square baking pan with parchment paper.

Add about ⅔ of the crisp to the bottom of the pan and using your fingers or a spatula, press the crisp down into the pan firmly to create an even layer. 

Add in the blueberry filling and spread it out evenly. 

Add the reaming crisp on top in an even layer. It’s okay if there are a few holes here and there on top. 

Bake for 45-50 minutes or until the top is golden brown. 

Remove from the oven and let it cool completely before cutting. After it is almost completely cooled, add it to the fridge for an hour or two to help it stay in a bar shape. 

When it is completely cool, lift the bars out of the pan with the parchment paper. Remove the parchment paper and cut into 9 squares. And enjoy!