Stir in graham cracker crumbs, shredded coconut, and chopped walnuts until combined. Press mixture into the pan and chill for 15 minutes.
Melt semisweet chocolate chips with oil in a microwave-safe bowl (heating in 10-second bursts), or a double boiler, stirring until smooth. Pour the melted chocolate over the set filling.
Chill in the refrigerator for an additional 30 minutes, or until the chocolate is firm. Once fully set, use a warm, sharp knife to cut the dessert into bars.