01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, allowing overhang for easy removal.
02 - In a large bowl, combine flour, oats, both sugars, melted butter, shredded coconut, salt, baking powder, and vanilla extract. Mix until crumbly and well combined.
03 - Press two-thirds of the crumble mixture firmly into the bottom of the prepared pan to create an even base layer.
04 - In a separate bowl, gently toss blueberries with lemon juice, sugar, and cornstarch until evenly coated.
05 - Spread the blueberry mixture evenly over the pressed crumble base.
06 - Sprinkle the remaining crumble mixture over the blueberries, pressing down gently.
07 - Bake for 35-40 minutes until the top is golden brown and the blueberry filling is bubbly.
08 - Allow bars to cool completely in the pan before cutting into squares for serving.