Heat oven to 350°F. Spray bottom only of 9x5-inch loaf pan with cooking spray. Place 2 cups cereal in resealable food-storage plastic bag or between sheets of waxed paper; crush with rolling pin to make 3/4 cup. Set aside.
In large bowl, beat sugar and oil with electric mixer on low speed until well mixed. Beat in buttermilk, vanilla and egg just until blended; beat in bananas. Stir in flour, cocoa, baking soda and salt until well mixed. Stir in 3/4 cup crushed cereal and chocolate chips. Spoon and spread evenly in pan.
Place 1/2 cup cereal in resealable food-storage plastic bag or between sheets of waxed paper; coarsely crush with rolling pin. Sprinkle over batter in pan; press lightly.
Bake 1 hour 10 minutes to 1 hour 20 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes. Remove from pan to cooling rack. Cool completely, about 2 hours.