Preheat oven to 350ºF. Prepare an 8 or 9-inch baking dish with parchment paper or foil and nonstick cooking spray.
In a large bowl, whisk together the mashed banana, sugar, honey, oil, vanilla, and egg. Add flour, salt, cereal, chocolate chips, and walnuts. Stir until well combined. Pour batter into prepared baking dish. Bake at 350°F for 20 to 25 minutes or until a toothpick inserted into center comes out clean. Cool completely, then cut into bars.
Store bars in an airtight container at room temperature for up to four days.