1. Cut pork in 1 1/2 inch cubes. Heat oil in a heavy pan and brown pork quickly.
2. Bring water to a boil in another pan. Slice and crush ginger root. Add to pork along with soy sauce. Simmer, covered, 1 hour. Skim off and reserve a ladleful of fat.
3. Add sugar and sherry to pan and simmer, covered, 30 minutes more.
4. Wash spinach and remove tough stems. Heat reserved fat. Add spinach and stir-fry until softened but still fresh and green.
5. Line a serving dish with spinach, top with pork cubes, pour gravy over, and serve.