HEAT oven to 350° F. Coat 13x9-inch baking pan with no-stick cooking spray.
BEAT cake mix, cinnamon, eggs, water and oil in medium bowl with an electric mixer on medium speed for 2 minutes, scraping bowl occasionally. Beat in mashed bananas. Stir in nuts. Spread in prepared pan.
BAKE 34 to 36 minutes or until toothpick inserted in center comes out clean. Cool 45 minutes. Serve warm. Top each serving with sliced bananas. Drizzle with caramel syrup.