Preheat oven to 350F degrees. Spray the bottoms of (two) 8x4-inch loaf pans with nonstick cooking spray.
In a large mixing bowl mix together the cake mix, pudding mix, water, eggs and oil. Stir well until combined.
Pour half the bread batter into each prepared loaf pan (a quarter of the total batter into each loaf pan.)
In a smaller bowl, combine softened butter, brown sugar and cinnamon. Mix together until combined.
Spoon half the cinnamon butter mixture onto the batter in each loaf pan and swirl (a quarter of the total mixture into each loaf pan.)
Pour the remaining bread batter evenly on top of each loaf pan, and again, swirl in the remaining cinnamon butter mixture between both loaves.
Bake for 45-50 minutes until a toothpick inserted in the middle comes out clean.
Let cool for 10 minutes before removing from the pan and placing on a cooling rack. Allow the breads to finish cooling on the rack.
In a small bowl mix the powdered sugar with water or milk and mix well. You want this to be a thick but drizzable consistency so you may need to add another tablespoon of water.
Drizzle the icing on the top of both bread loaves.