Heat oven to 375° F. In a small bowl, mix graham cracker crumbs, flour and baking powder. In a large mixer bowl, beat sweetened condensed milk and butter until smooth. Add graham cracker crumb mixture; mix well. Stir in coconut, chocolate chips and walnuts. Drop by rounded tablespoons onto ungreased cookie sheets. Bake 9 to 10 minutes or until lightly browned. Store loosely covered at room temperature.