Preheat the oven to 350.
Zest the whole rind of a lemon. Set aside in a bowl.
In a stand mixer, combine cake mix, pudding, eggs, and oil.
Juice lemon into a one-cup measuring cup and fill the rest of the way with water.
Pour into a mixing bowl.
Mix together all ingredients, beat on medium to high until batter is light and fluffy.
Spray a bundt pan or 2 loaf pans with non-stick spray.
Pour batter into a pan and spread evenly.
Cook for 35-45 minutes or until an inserted toothpick comes out clean.
Remove from oven and let rest for 3 minutes.
Invert on to serving platter or stand.
In a small bowl, mix together lemon zest, powdered sugar and 1/4 cup water.
If icing is too runny, add a little bit of powdered sugar. If it's too thick, add a tiny bit of water...just a little at a time to get the right texture.
Spoon icing over cake while it is still warm.
Allow cake to cool to room temperature before covering.