Preheat oven to 375. Prepare a 13" x 9" pan with cooking spray and flour; set aside. To prepare topping, combine half cup cake mix, oats, and two tablespoons margarine in a mixing bowl. Mix until crumbly; set aside. To prepare base, combine remaining cake mix, eggs, water, and remaining margarine. Spread into bottom of prepared pan. In another mixing bowl, mix cranberry sauce until smooth. Spread over base in pan. Sprinkle with reserved topping. Bake for 35 mintues, or until lightly browned on top.