Preheat oven to 350 degrees.
Grease and flour a 13 x 9 inch pan.
In large bowl, combine cake mix, bananas, water, oil, and eggs.
Beat at low speed until moistened; beat 2 minutes at high speed.
Pour batter into prepared pan.
Bake for 30 - 40 minutes or until toothpick inserted in center comes out clean.
Cool completely.
In a small bowl, combine frosting and mashed bananas.
Spread over cooled cake.
In small bowl, combine melted chocolate and powdered sugar.
Add water until desired consistency, blending until smooth.
Drizzle over frosting.
Store in refrigerator.