Lightly grease a 13-by-9-inch baking pan with cooking spray or use extra blood orange EVOO.
Melt marshmallows and olive oil together in a large saucepan over low heat, stirring occasionally, until completely melted. Remove from heat and fold in cereal, gently turning the mixture until completely coated. Press into prepared pan using fingers or spatula. Place in refrigerator for at least 1 hour before cutting into squares.
