Wash napa cabbage thoroughly and cut into bite-sized pieces.
Cut duck meat into pieces suitable for eating.
Slice onion, green onion, and spicy green chili peppers.
Place duck meat in a pan and stir-fry over medium heat until the fat is rendered.
When the duck meat is cooked, add napa cabbage, onion, green onion, and green chili peppers.
Add soy sauce, red pepper flakes, minced garlic, ginger, and black pepper for seasoning.
Cover and steam over low heat for 10 minutes.
Taste and adjust seasoning with salt if necessary once ingredients are cooked.
Transfer to a serving dish.