Preheat oven to 325 degrees and spray an 8x8 baking pan with nonstick spray. In a large bowl, using a hand blender, mix together the eggs, oil and water. Slowly add the dry brownie mix and blend until a thick batter forms.
Evenly spread half of the batter onto the bottom of the prepared pan. Place the chocolate sandwich cookies on the top of batter, covering the surface completely. Pour remaining batter over the cookies, spreading evenly.
In a microwave safe bowl, heat the chocolate hazelnut spread until pourable, about 30 seconds. Drizzle over top of brownies, then swirl into the batter using the back of a spoon.
Bake 25-30 min then cool completely on a wire rack. Cut into 16 brownies.