Preheat the oven to 350°F.
In a bowl, mix the melted butter with the graham cracker crumbs. Press the mixture onto the bottom of a 9-inch pie dish. Layer the coconut, walnuts, chocolate chips, and marshmallows over the crust. Drizzle the condensed milk evenly over the top.
Bake for 25 to 30 minutes, or until the marshmallows are golden brown. Melt the semisweet chocolate in the microwave, being careful not to overheat. Dip a fork into the chocolate and flick or drizzle over the finished pie.
Chill in the refrigerator.