Preheat oven to 325. Prepare two 4 1/2" x 8 1/2" pans with cooking spray and flour; set aside. In a mixing bowl, combine cake mix, pumpkin pie spice, baking soda, pumpkin, pineapple, eggs, and walnuts. Mix well. Spoon batter evenly into prepared pans. Bake for 45 minutes, or until toohpick inserted in center comes out clean. Cool in pans 20 minutes before removing.