Preheat oven to 350 degrees.
Grease or spray a 9 x 5 loaf pan with cooking spray.
In the bowl of a stand mixer, Pour cake mix, pudding, melted butter, eggs, and water. Mix for 2 minutes.
In a seperate bowl, combine brown sugar and cinnamon and stir with a spoon.
Pour 1/3 of cake batter into the loaf pan.
Sprinkle a layer of the brown sugar and cinnamon mixture on top of the batter.
Pour another layer of cake batter on top.
Top with another layer of brown sugar and cinnamon mixture.
Top with the last layer of cake batter.
Using a butter knife, swirl the cake batter and cinnamon mixture. See photo above.
Lightly sprinkle brown sugar and cinnamon mixture on top of cake as desired.
Bake for 50 to 55 minutes. You can check for doneness with a toothpick. TIP: If your cake looks like it is getting too brown on top, lay a piece of foil over cake for the rest of the cooking time.
In a medium size bowl, mix powdered sugar and milk with a spoon or whisk.
Let cake cool for 10 minutes and top with icing.