In small bowl, combine crushed wafers and margarine. Press mixture firmly onto bottom of dessert dish.
In medium mixing bowl, beat the marshmallow creme, mint extract, and green food coloring with an electric mixer on medium speed til smooth. Fold in 1/2 cup of the semisweet chocolate pieces.
In small mixing bowl, whip creme til soft peaks form; fold in marshmallow creme mixture. Spread over crust in the dessert dish.
Sprinkle remaining semisweet chocolate pieces over dessert. Apply lid and freeze for at least 6 hours.
At serving time, remove from freezer and let stand for 10-15 minutes. For easy serving, place warm, moist cloth on the bottom of the dish.
Cut the squares with a table knife by applying light pressure.