
Preheat your oven to 375°F (190°C) and line an 8-inch square baking pan with parchment paper.
In a large bowl, combine the oats, flour, brown sugar, baking soda, salt, and cinnamon (if using). Mix well.
Stir in the melted butter and vanilla extract until crumbly for the base of your bars.
Press half of the oat mixture into the bottom of the prepared pan.
In a separate bowl, toss the blueberries with granulated sugar and cornstarch. Spread this mixture over the oat base.
Crumble the remaining oat mixture over the blueberries, gently pressing down.
Bake for 35-40 minutes or until golden brown and bubbly.
Allow to cool completely, then lift out and cut into squares.