Preheat your oven to 350°F (175°C) and grease and flour two 9-inch round cake pans.
In a large bowl, combine the white cake mix, key lime juice, vegetable oil, eggs, and lime zest. Mix until well combined.
Pour the batter into the prepared cake pans and bake for 25-30 minutes, or until a toothpick inserted into the centre comes out clean.
Allow the cakes to cool completely before removing them from the pans.