Microwave chocolate in microwaveable bowl on HIGH 1 to 2 min. or until chocolate is almost melted, stirring after 1 min.; stir until completely melted.
Mix next 3 ingredients in large bowl. Beat eggs in medium bowl; stir in melted chocolate, sugar, buttermilk, 1/2 cup oil and banana.
Add to flour mixture; stir just until moistened. (Batter will be lumpy.) Stir in 2 cups cereal.
Pour into 9x5-inch loaf pan sprayed with cooking spray. Crush remaining cereal in small bowl.
Drizzle with remaining oil; mix well.
Sprinkle over batter in pan.
Bake 50 to 55 min. or until toothpick inserted in center comes out clean. Cool 10 min.; remove to wire rack. Cool completely.