1Heat oven to 350°F (325°F for dark or nonstick pan). Grease bottom only of 13x9-inch pan. In large bowl, beat cake mix, water, oil, whole eggs and mashed bananas with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Stir in chocolate chips. Pour into pan.
2Bake 38 to 42 minutes or until toothpick inserted in center comes out clean. Cool 15 minutes.
3In small microwavable bowl, microwave frosting uncovered on High 20 seconds; stir. Microwave 5 to 10 seconds longer or until very soft and smooth; spread evenly over cake. Garnish as desired. Store loosely covered.