Lightly spray (1) 9x13-inch pan with nonstick cooking spray. To the pan, add the blueberries, sugar, lemon zest, and vanilla. Stir to combine, then spread the blueberries evenly into the pan.
4 cups fresh or frozen blueberries, ½ cup granulated sugar, Zest of 1 large lemon, 1 teaspoon vanilla extract
Sprinkle the dry cake mix evenly over the blueberries. Slowly drizzle the butter over the top of the cake mix.