Line the bottom of an 8×8 pan with parchment paper and spray with cooking spray for easy removal.
To make the crust & crumble, in a large bowl add melted butter, flour, oats, honey, brown sugar, lemon zest and salt. Mix until just combined, mixture should be a little crumbly. Scoop out 1 cup of the mixture and set aside, that will be your crumble.
Add the remaining mixture to the prepared pan. Spread the mixture out and using your fingers press into the bottom of the pan so the crust is in an even layer.
To make the Blueberry Filling: in a small bowl stir blueberries, brown sugar, lemon zest, and corn starch. Toss to combine.
Pour the blueberry mixture on top of the crust and spread out evenly.
Evenly sprinkle the crumble mixture over the top of the bars.
Dust the top of crumble with cinnamon (optional).
Bake the bars for 50 minutes. Remove the bars from the pan and let sit for 10 minutes. Cut and serve.
Recipe adapted from Blueberry Oatmeal Crumble Bars by Averie Cooks.