Preheat the oven to 350 degrees.
In a 9 x 13-inch glass baking dish, melt the butter or margarine in the microwave.
Sprinkle the graham cracker crumbs evenly over the melted butter or margarine.
Pour the sweetened condensed milk evenly over the crumbs.
Sprinkle the shredded coconut, chocolate chips and walnuts or pecans evenly over the sweetened condensed milk layer; press down gently with your hand or the back of a rubber spatula.
Bake for 25–30 minutes or until lightly browned.
Let cool in the pan on a wire rack for 30 minutes. Cut into 24 bars.