Mix graham crumbs and butter, press evenly into a 13" x 9" pan lined with parchment paper. Pour can of condensed milk over crumb base. Sprinkle chocolate chips, coconut, and nuts over base.
Bake in a preheated oven 350°F for 25 minutes.
Melt chocolate in microwave on low, stir chocolate till smooth.
Remove pan from oven, top with marshmallows, and drizzle with melted chocolate.