Place graham crackers in a sandwich bag and crush with a rolling pin until you have 2 cups of crumbs. Mix the crumbs well with the melted butter. Spray an 8 x 8 baking dish with cooking spray and pat the crumb mixture into the bottom of the dish. Bake this in a preheated 350 degree oven for 10 minutes. Mix the milk with the coconut in a bowl using a spoon. Spread over graham cracker crust and return to 350 degree oven for 15 more minutes. Remove and sprinkle chocolate chips and nuts over the top. Return to 350 degree oven about 5 more minutes or just until chocolate chips are warm enough to spread with a knife. Let cool in refrigerator. Cut into small squares. Makes about 30 pieces depending on what size you cut the bars