Prepare and bake Pretzel Crust; set aside to cool.
For filling, in a small saucepan soften gelatin in the cold water. Cook and stir over low heat just until gelatin dissolves.
Meanwhile, in a chilled bowl combine whipping cream and vanilla. Beat with chilled beaters of an electric mixer on medium speed until soft peaks form. Keep chilled (do not hold longer than 30 minutes).
Remove gelatin from heat; transfer to a large mixing bowl. Stir in egg product, sugar, lemonade concentrate, lime peel and juice, tequila, and, if desired, green food coloring. Chill until mixture just begins to mound when spooned, stirring occasionally (the gelatin sets up quickly, about 5 to 6 minutes).
Beat gelatin mixture with an electric mixer on medium to high speed for 4 minutes. Immediately fold the whipped cream into gelatin mixture. Chill again until mixture mounds when spooned (about 1 to 2 minutes).
Spoon filling into Pretzel Crust. Loosely cover and chill for 4 to 6 hours or until firm. Garnish with Glazed Shredded Lime Peel, if desired, Serves 10.
Spray a 9-inch pie plate with nonstick spray coating. In a medium saucepan melt butter; stir in sugar. Add pretzels, then egg white, if using (egg white gives a firmer but less crunchy crust). Toss to mix well. Spread evenly into prepared pie plate. Press onto bottom and sides to form a firm, even crust. Bake in a 350 degree F oven for 7 to 9 minutes or until edge is lightly browned. Cool on a wire rack before filling.
Glazed Shredded Lime Peel
Shred the peel from the limes (you should have about 2 tablespoons peel). In a small bowl stir together water and refrigerated or frozen egg product. Dip shredded lime peel in egg mixture. Remove from mixture using a fork and allow to drain; place on waxed paper, separating shreds of peel. Sprinkle evenly with sugar. Let dry in refrigerator on waxed paper 2 to 4 hours.