Whisk together evaporated milk and next 2 ingredients in a bowl 2 minutes or until mixture is thickened.
Beat softened cream cheese and vanilla at medium speed with an electric mixer until fluffy. Add lemonade concentrate, beating until smooth. Add milk mixture and beat until blended. Pour mixture into crust.
Cover and chill 8 hours or until firm. Dollop each slice with whipped topping. Garnish with lemon zest or crushed lemon drops if desired.