Preheat oven to 350 degrees. Grease a 9-inch springform pan, and line the perimeter with a 3-inch wide strip of parchment paper.
Process coconut and lime zest in food processor until coarsely ground. Reserve 1/2 cup.
Add pretzels to remaining coconut mixture, and process until finely ground.
Add melted butter, and pulse to combine. Press mixture into bottom of prepared pan.
Bake until edges are golden, 10 to 12 minutes. Transfer pan to wire rack to cool completely.
For the filling, combine 1/4 cup water and gelatin in a small saucepan, and let sit until gelatin softens, about 5 minutes.
Add margarita mix, tequila, and triple sec, and cook over low heat, stirring frequently, until gelatin dissolves, about 5 minutes. Let cool 15 minutes.
Meanwhile, in bowl of stand mixer fitted with whisk, whip cream on medium-low speed until foamy. Then increase to high speed, and whip until soft peaks form. Transfer whipped cream to a bowl, and store in fridge until ready to use.
In clean bowl of stand mixer, whip condensed milk and cream cheese until combined. Add 1 cup margarita mixture, and whip until combined.
Fold in one-third of the whipped cream, and then fold in the remaining whipped cream.
Pour filling into cooled crust, and refrigerate for 1 hour.
Then, to make the topping, stir remaining 1/2 cup water into remaining margarita mixture. Pour mixture through a fine-mesh sieve into a 2-cup liquid measuring cup.
Pour topping over filling, and refrigerate until set, about 4 hours.
Remove sides of pan and parchment, and press reserved coconut mixture onto sides of cake, and top cake with lime slices. Serve.