Gather all ingredients. Preheat the oven to 350 degrees F (175 degrees C). Lightly grease a 10x15-inch baking pan with cooking spray.
Prepare oat streusel topping: stir oats, flour, brown sugar, and cinnamon together in a large bowl. Cut in butter with a pastry blender until the mixture is crumbly. Set aside.
For bars. whisk flour, baking powder, baking soda, and salt together in a bowl.
Whisk together white sugar and oil in a large bowl until well combined. Whisk in milk, eggs, and vanilla extract.
Stir flour mixture into egg mixture until just combined.
Gently fold in blueberries.
Spread batter evenly into the prepared pan.
Sprinkle streusel topping evenly over batter.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 25 to 28 minutes.
Let bars cool in the pan on a wire rack 20 to 30 minutes before slicing and serving Recipe developed by Barrett Heald
