Preheat oven to 325°.
Place wafers in a food processor; process until finely ground. Add sugar, margarine, and egg white; pulse 2 times or just until combined.
Press crumb mixture into bottom and up sides of a 9-inch round tart pan coated with cooking spray. Bake at 325° for 15 minutes or until lightly browned. Cool on a wire rack.
Combine grated lemon rind, juices, eggs, and milk in a bowl, stirring with a whisk until blended. Pour mixture into prepared crust. Bake at 325° for 30 minutes or until filling is set. Cool completely. Top with whipped topping. Garnish with lemon rind strips and mint, if desired.