Preheat your oven to 350 degrees F. Butter a 13x9-inch baking dish.
Add the blueberries to the baking dish. Stir in the orange zest and orange juice. Stir in the flour. Spread the blueberries out to form an even layer.
Spoon the cake mix out in an even layer over the blueberries.
Mix together the melted butter and buttermilk, then pour over the cake mix in an even layer. Tilt the pan as needed for butter and buttermilk to cover top evenly and cover the dry cake mix.
Bake the cake at 350 degrees F for 45-60 minutes or until golden brown and the blueberries are bubbling.
SNAPPY TIPS: Fresh orange zest and juice makes a big difference, so I don't suggest leaving it out. Some people have mentioned cake mixes with pudding do not have the best results so I'd suggest using a classic yellow cake mix without pudding.SNAPPY SUBSTITUTIONS: Instead of buttermilk you could substitute milk. Instead of blueberries you could use other types of fruit.