In a large microwave-safe bowl, combine butter, cocoa and sugar and microwave on high for 45 seconds. Stir, and microwave on high another 20-30 seconds if necessary so that all is melted and combined. Let cool 5 minutes.
Quickly whisk in egg (mixture will thicken as the egg is incorporated). Stir in coconut and graham crumbs until combined.
Press into an 8x8" pan lined with tin foil.
FILLING
With an electric mixer, beat butter until smooth. Add powdered sugar and 2 tablespoons milk and beat until smooth, adding a bit more milk or sugar to reach desired consistency. Add extract and green food coloring (as desired).
Spread over base in pan.
GANACHE
In a medium microwave safe bowl, combine chocolate and butter and melt in 20 second intervals on high, stirring each time, until smooth.
Pour over filling in pan. Refrigerate until completely set, at least 2-3 hours, before slicing and serving. Store in the refrigerator or freeze for up to a few months.