1. Preheat oven to 350°F. Spray a loaf pan with non-stick cooking spray. 
2. Measure out 1 cup of Key Lime Lemonade, set aside. In a large bowl or stand mixer fitted with a paddle attachment, add cake mix, eggs, oil, zest of 1 lime, and the 1 cup of Key Lime Lemonade. Beat on medium speed for 2 minutes. 
3. Pour batter into prepared pan. Place in oven for 30-40 minutes, or until golden brown and inserted toothpick comes out clean. 
4. While the cake is baking, add powdered sugar, lime zest, and 3 tbsp of the remaining Key Lime Lemonade to a medium bowl. Whisk until all the sugar has dissolved and you are left with a fragrant glaze. Set aside and enjoy any leftover Key Lime Lemonade! 
5. When the cake is done, allow to cool for 10 minutes, then remove from the pan. Place on a cooling rack that is set in a baking sheet, allow to cool for an additional 5-10 minutes. Take your bowl of Key Lime Glaze (whisk briefly if it has hardened), and drizzle glaze all over the loaf.  
6. Slice and serve immediately. Store any leftovers in an airtight container in the fridge for up to 3 days.