Preheat the oven to 350F degrees (or 325F degrees if using a glass pan). Grease and flour the bottom and sides of a 9x13 inch pan.
Add the cake mix, eggs, sour cream, 1/2 c oil, lime juice and lime zest to a large bowl.
Beat with an electric mixer until smooth.
Pour the batter into the prepared pan and bake for 27-32 minutes or until an inserted toothpick comes out clean and if you give the pan a gentle nudge the cake doesn't wobble in the middle.
Remove from the oven and allow to cool.
In a small saucepan over low heat add the lime juice and sugar. Heat until the sugar dissolves while gently stirring.
When the cake is out of the oven, take a small pastry brush or a spoon and brush/drizzle the syrup over top.
Spread the whipped topping over top of the cooled cake. Then sprinkle with lime zest.
Cut into slices and serve.
*If making the cake ahead of time, make the cake the night before and drizzle with the lime syrup. Cover tightly and leave at room temperature over night. Add the whipped topping before serving.
**Once the cake has been decorated with whipped topping or whipped cream, cover and store in the fridge.