Heat oven to 350°F. Spray 13x9-inch pan with cooking spray. On ungreased cookie sheet with sides, bake walnuts at 350°F. for 5 minutes.
Remove cookie sheet from oven. Stir coconut into walnuts. Return to oven; bake an additional 4 to 6 minutes or until coconut is light golden brown, stirring twice during baking. Set aside to cool.
In 4-quart saucepan or Dutch oven, melt butter over medium heat. Add marshmallows; cook 4 to 6 minutes, stirring constantly, until melted. Stir in cocoa until well blended. Remove from heat.
Stir in cereal, banana chips, toasted walnuts and coconut until evenly coated; pour into sprayed pan. Spread mixture evenly, pressing down slightly. Cool 30 minutes. Cut into bars.