In bowl, stir together graham crumbs, coconut, walnuts, cocoa powder and sugar. Drizzle with butter and stir until combined. Press into bottom and up side of 9-inch (23 cm) pie plate. Bake at 350 degrees for 5 minutes. Allow to cool completely.

Allow ice-cream to soften on counter for 15 minutes. Fold custard powder into ice cream; spread over crust, smoothing top. Cover surface directly with plastic wrap; freeze until firm, 2 to 3 hours.

In small saucepan, heat chocolate and cream over medium-low heat, stirring occasionally, until melted and smooth. Let cool for 5 minutes. Spread over top of pie; freeze until firm, about 20 minutes.
Once firm, cover with plastic wrap and freeze for at least 12 hours in advance of serving to allow the ice-cream to harden.

Let stand for 10 minutes before slicing. Run the blade under hot water, drying on a towel to assist cutting through the ice cream into neat slices.