Melt the butter or margarine in a 20x30cm baking dish. Sprinkle the biscuit crumbs evenly over the butter. Sprinkle over the chocolate chips. Cover with the coconut. Sprinkle the walnuts on top of the coconut layer. Finally, pour the condensed milk over everything as evenly as you can.
Bake for 30 to 35 minutes in the preheated oven. Cool and cut into bars.