For bottom layer.....
In saucepan, combine 1/2 c margarine and the cocoa. Heat and stir until well blended.
Remove from heat; add 1/2 c powdered sugar, egg, and vanilla. Stir in Graham cracker crumbs. Mix well. Press into the bottom of a 9x13 baking pan.
Melt another 1/2 c margarine, In small mixing bowl, combine melted margarine, and Creme De Menthe. at low speed, beat in remaining 3 c powdered sugar until smooth. Spread over the crumb layer. Chill for 1 hour.
In small saucepan, combine the remaining 1/4 cup margarine and chocolate chips. Cook and stir over low heat until completely melted.
Spread over mint layer, chill 1-2 hours, cut into small squares and store in refrigerator.