Toss the beef with lime juice, salt, and pepper. Let it stand for 30 minutes.
Brown the beef in oil in a large stockpot. Add enough water to cover, bring to a simmer, and cook until tender, about 60 minutes.
Build the Soup:
Blend the pumpkin puree with 2 cups of the stock until smooth, then add it to the pot with the remaining stock, onion, garlic, carrots, potatoes, and celery.
Simmer until the vegetables are nearly tender. Add the cabbage and pasta and cook until both are tender.
Serve:
Stir in the scallions, taste for seasoning, and ladle the soup into warm bowls.
Notes
A few sprigs of thyme or parsley can be simmered with the broth and removed before serving.
The soup should be thick but pourable; add stock if it becomes too dense.