Heat the oven to 350 degrees F. Spray an 8- or 9-inch square pan lightly with nonstick cooking spray, then line with parchment paper.
In a large mixing bowl, combine the brownie mix, eggs, oil, water, and Nutella. Stir with a wooden spoon until just mixed. Spread into the prepared pan.
Bake 25 to 30 minutes or until inserted toothpick comes out nearly clean. Cool the brownies completely before frosting.