Preheat the oven to 350°F (175°C). Grease a Bundt pan well with non-stick spray.
In a small bowl, mix the cinnamon and sugar. Sprinkle a couple spoonfuls into the greased Bundt pan, rolling it around to coat the bottom and sides.
In a large mixing bowl, beat together the cake mix, pudding mix, eggs, oil, water, and vanilla extract until smooth—about 2 minutes.
Pour half the batter into the prepared pan. Sprinkle some of the remaining cinnamon sugar on top.
Add the rest of the batter, and finish off with the last of the cinnamon sugar.
Bake for 40–45 minutes or until a toothpick comes out clean. Let it cool in the pan for 10 minutes, then flip it out onto a wire rack.
Let cool completely before slicing (or sneak a warm slice—you earned it).