Preheat Oven:
Preheat your oven to 350°F (180°C). Grease and flour a 9-by-13-inch rectangular baking dish with butter or use nonstick cooking spray.
To prepare the cake batter:
In a large bowl, combine the cake mix, instant pudding, oil, water, eggs, vanilla extract, and lemon zest. Beat with an electric mixer at medium speed for 2–3 minutes until smooth and blended.
To bake the cake:
Pour the batter into the prepared pan and spread evenly with a spatula. Bake for 30 to 35 minutes or until a toothpick inserted in the center comes out clean.
To cool:
Remove the cake from the oven and let it cool slightly in the pan on a wire rack.
