Preheat oven to 350°F (175°C) and line a cupcake tin with paper liners.
In a large bowl, combine the cake mix, eggs, oil, margarita mix, water, lime zest, and tequila. Mix until smooth.
Divide the batter evenly among the cupcake liners and bake for 18–20 minutes or until a toothpick comes out clean.
Let cupcakes cool completely before frosting.
In a separate bowl, beat the butter until fluffy. Gradually add powdered sugar, then mix in the margarita mix and lime juice.
Frost the cooled cupcakes and garnish with fresh fruit if desired.