Preheat oven to 325 degrees.
Grease the Bundt pan with butter or use baking spray.
In blender or mixing bowl add the eggs, milk, oil or butter, vanilla, ground cinnamon and blend these ingredients on medium speed for about 1 minute or mix until well combined.
Then, and cake mix to the mixing bowl.
Blend on medium speed or mix just until well combined.
Gently fold in the mashed bananas and chopped walnuts.
Pour the batter into the Bundt pan.
Depending on your oven temperature, bake for 50 minutes to 1 hour or until a toothpick comes out clean when inserted into the middle of the cake.
Remove the pan from the oven.
Let it cool completely in the pan on a baking rack, and then remove it from the pan.
Sprinkle powdered sugar on top of loaf immediately before serving.