In a small bowl add the streusel ingredients. Mix with a fork until combined. I've found if the butter is slightly melted, this step goes better.
In a larger bowl add the cake mix, cream cheese, eggs, water and oil. Mix together with a hand mixer until smooth, don't over mix though.
Spray a 9x13 pan with non-stick spray. Add half of the batter to the pan, spread out evenly. Sprinkle over the blueberries. Add remaining batter and spread on top of blueberries.
Sprinkle over the struesel.
Place in the oven on the center rack. Bake for 45 minutes or until a toothpick comes out clean when inserted in the middle of the cake. Place on a cooling rack. Serve warm or room temperature. Enjoy!