Preparation: Preheat the oven to 350 °F (200 °C).
Spray the bottom only of a 9 x 5 inch (22 x 33 cm) loaf pan with cooking spray.
Place 2 cups (80 g) of cereal in a large plastic bag or between two sheets of wax paper; crush with a rolling pin to get ¾ cup of crushed cereal. Set aside.

In a large bowl, beat the sugar and oil with an electric mixer at low speed until well combined.
Beat in the buttermilk, vanilla, and egg, then the bananas, until the mixture is smooth.
Beat in the flour, cocoa, baking soda, and salt until combined.
Stir in the crushed cereal and chocolate chips.
Spoon the mixture into the prepared loaf pan; smooth the top.

Place ½ cup (20 g) of cereal in a large plastic bag or between two sheets of wax paper; coarsely crush with a rolling pin.
Sprinkle over the batter in the loaf pan; gently press in.

Bake for 1 hour 10 minutes to 1 hour 20 minutes, or until a toothpick inserted into the center comes out clean.
Let cool for 10 minutes. Remove from pan and transfer to a wire rack.
Let cool completely, about 2 hours.