In large mixing bowl, combine cake mix and soda. Add water, eggs, and bananas. Beat 4 minutes on medium speed of electric mixer. Fold in nuts. Pour into greased and floured 2-qt. Mold. Place on bottom of slow-ooking pot. Cover cake with 4 to 5 paper towels. Cover pot and cook on high for 2 to 3 hours. Invert on cooking rack. Serve plain, dusted with powdered sugar, or drizzled with a thin glaze.