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.
Sprinkle the dry cake mix evenly over the blueberries. Slowly drizzle the butter over the top of the cake mix.
Bake for 1 hour, or until the top is golden brown and the blueberries are bubbly. Let cool for 10-15 minutes before serving.
Notes
If you don’t like the combination of lemon and blueberries, use a yellow cake mix and try swapping the lemon zest for 1 teaspoon ground cinnamon.