Camilla knocked up a mozzarella salad with blood oranges, beetroots, leaves and watercress at the CEO CookOff event in the City of London.
About 400 "unsung heroes" enjoyed a three-course meal, with mains including roast lamb and wild mushroom ravioli.
The duchess is patron of the newly formed UKHarvest charity.
The organisation collects surplus food from supermarkets, restaurants and manufacturers, turning it into meals for families and individuals in need.
The duchess was joined by former Spice Girl Emma Bunton, presenter Jamie Theakston and 100 UK chief executives at the former Billingsgate Market building. She was paired with Peter Harding from Lucozade Ribena Suntory for the cook off.
"It's looking good so far," said Oliver - who advised the duchess to make the cheese the heart of her salad, while encouraging her to use her hands.
Oliver, whose food foundation co-hosted the event, applauded Camilla's efforts.
All done?  The celebrity chef's verdict on Camilla's cooking skills - "She's got the touch".
The Duchess of Cornwall has helped top chefs create a banquet from produce that would otherwise go to waste - under the watchful eye of Jamie Oliver.