Preheat oven 375 degrees F. Spread melted butter at the base of a 9x13 and set aside.
In a medium bowl, toss blueberries, sugar, cornstarch, lemon zest, and salt.
In a large bowl, mix almond milk, ground flaxseeds vanilla, set aside for about 5 minutes.
Add the all-purpose gluten-free flour, cane sugar, baking powder, salt.
Add the almond mixture to the dry ingredients and mix well to combine.
Spread the batter into the prepared baking dish and spread evenly.
Spread the blueberries on top of the batter.
Bake for 40 minutes or until a toothpick inserted in the center comes out clean.