Begin by preheating your oven to 350°F (175°C). Prepare a 9x13-inch baking dish by lightly greasing it to ensure easy removal of the cake.
In a large mixing bowl, combine the yellow cake mix, pumpkin puree, eggs, sugar, vegetable oil, water, and cinnamon. Stir the ingredients thoroughly until the batter is smooth and well incorporated.
Pour the prepared batter into the greased baking dish, spreading it evenly. Place the dish in the preheated oven and bake for approximately 45 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Notes
Alternatively, this recipe can be baked in two 9-inch round cake pans.