Preheat the oven to 400 degrees F (200 degrees C). Grease an 8x8 inch baking dish.
In a medium bowl, stir together the graham cracker crumbs and coconut. Pour in the condensed milk and melted margarine, mix until well blended. Press the mixture evenly into the prepared pan.
Bake for 10 to 12 minutes in the preheated oven. Remove and let cool. Melt chocolate bars in a microwave or over a double boiler, stirring occasionally until smooth. Spread over the cooled bars, chill and cut into squares.