According to the query on Gourmet World: The reasons and solutions for duck meat turning green after being cooked are as follows:

Cause: oxidation reaction. During the cooking process of duck meat, the ferrous iron in it The ions may react with oxygen in the air to form green ferrous oxide. This green color may be caused by tiny particles distributed in the duck meat, which makes the duck meat appear green. Some cookware may dissolve copper ions due to the action of copper ions, and the protein in duck meat will combine with copper ions to produce a green color. Bacterial contamination. If duck meat is contaminated with bacteria during storage or processing, it may cause the duck meat to turn green.

Solution: Choose fresh duck meat. When buying, choose fresh and shiny duck meat. Avoid buying duck meat that is green in color or has mucus on the surface. Before cooking, blanch the duck meat in boiling water or marinate it with ginger, garlic and other seasonings for a period of time to help eliminate bacteria and odor in the duck meat. Use appropriate cookware, avoid using cookware that may contain copper ions, and try to use stainless steel, ceramic and other cookware. To adjust the cooking method, you can try changing the cooking method, such as braising, stewing, etc., to avoid direct exposure of duck meat to oxygen.