Crush 20 oreos and place in 9x13 pan. Melt margarine and chocolate over medium heat. Remove & add beaten eggs & sugar. Pour over Oreo crumbs. Freeze for 1/2 hour. While waiting, combine ice cream with creme de'menthe until well combined. Pour over frozen crust. Sprinkle with remaining 10 crushed Oreos. Refreeze and serve.