Pre-heat oven to 325 F. Line a 10" x 14" baking pan with aluminum foil. Set aside.
Beat Baker's Best margarine, sugar and oatmeal until well blended. Stir in chopped pistachios and dried mangoes. Gradually add flour to form a soft dough. Press mixture evenly at the bottom of the prepared pan.
Bake in pre-heated oven for 20 - 25 minutes. Cool completely in the pan.Beat Baker''s Best margarine until light. Add confectioner's sugar and warm water. Lastly, add brandy and beat until smooth. Spread glaze evenly on top of cooled crust and let it set.
Drizzle with melted chocolate and top with pistachios.