Wash ham hock, and place in a 10-quart Dutch oven. Add water, onions, and pepper pod; bring to a boil. Reduce heat, and simmer 1 hour or until meat is tender.
Add mustard greens and salt to Dutch oven; bring to a boil. Cover; reduce heat and simmer 2 hours or until greens are tender. Drain, reserving 1 1/2 cups pot likker. Remove pepper pod; discard.
Transfer mustard greens to a serving dish. Pour pot likker over top, and garnish with onion rings and grated egg.