Rinse lean pork under running water; Pat-dry it with kitchen paper; Slice it; Put it in a mixing bowl; Marinate it with seasonings for 30 minutes.
Discard any salted charcoal paste of salted duck eggs; Rinse them.
Rinse, drain, peel and slice ginger.
Rinse mustard greens under running water thoroughly; Drain them; Trim a bit off the bottoms; Discard any wilted outer leaves; Cut the remaining into pieces.
Fill a stockpot with 2.5L water; Add the ginger; Bring to the boil over a high heat; Add the mustard greens, 3 tsp oil and the salted duck eggs; Bring to the boil over a high heat again; Turn to a medium heat; Cook over a medium heat for 15 minutes; Add the lean pork; Bring to the boil over a high heat again; Turn off the heat; Arrange the soup into serving bowls; Ready to serve.