Preheat oven to 350°F. Line two cupcake tins with paper liners. Set aside.

In a large bowl, mix together cake mix, margarita mix, oil, eggs and lime zest using a mixer or whisk until evenly moistened.

Fill cupcake tins until 2/3 full. Bake in preheated oven for approximately 20 minutes until lightly golden and toothpick inserted in the center comes out clean. Cool in pan 5 minutes then remove to wire rack to cool completely.

In the bowl of a stand mixer fitted with a paddle attachment, beat butter until light and fluffy. With the mixer running on medium-low speed, slowly add half the powdered sugar and continue beating until incorporated. Add tequila, margarita mix and lime zest. Mix for 1 minute on low then slowly add remaining powdered sugar until desired consistency is reached. You may not use all the powdered sugar. Add a drop of food coloring, mix. Add more coloring until desired shade is reached.

Frost cooled cupcakes with prepared frosting. Sprinkle with salt or sugar and top with each with a slice of lime.