Preheat your oven to 350°F (175°C) and grease a 9x9-inch baking pan or line it with parchment paper for easy removal.

In a large mixing bowl, combine the rolled oats, flour, brown sugar, baking powder, salt, and cinnamon. Mix well.

In a separate bowl, whisk together the melted butter, honey (or maple syrup), and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and stir until just combined. The mixture will be crumbly.

Reserve about 1 cup of the mixture for the topping, and press the remaining mixture firmly into the bottom of the prepared baking pan.

Evenly distribute the blueberries over the pressed oat mixture.

Crumble the reserved oat mixture over the blueberries to create a topping.

Bake in the preheated oven for 25-30 minutes, or until the top is golden brown.

Allow the bars to cool in the pan for at least 10 minutes before slicing into squares. For best results, cool completely before serving.