Spray a 9-inch deep dish pie pan with cooking spray. In a medium bowl, stir together pretzel crumbs, sugar, and melted butter.
Press pretzel crumb mixture into the bottom and up the sides of the pie pan. Refrigerate for at least 1 hour or freeze for 30 minutes.
Use a hand-held electric mixer to beat cream cheese until smooth.
Beat in Margarita mix and sugar.
Beat in 1 container of Cool Whip and tequila. Transfer mixture to pie crust. Note: You may have a little extra filling but most of it should fit.
Freeze for at least 6 hours.
Use a pastry bag with a large star tip to pipe the remaining Cool Whip around the outside edge of the pie. Note: Instead you can spread the Cool Whip in an even layer on top of the pie.
Sprinkle with lime zest and garnish with lime slices.