In a large pot, combine the beef, water, salt, black pepper, onion, and garlic. Bring to a boil over medium-high heat, then reduce to a simmer. Cover and cook for about 1.5 to 2 hours, or until the beef is tender. Skim off any foam that rises to the surface.

Once the beef is tender, add the carrots, potatoes, zucchini, and corn to the pot. Continue to simmer for another 30 minutes, or until the vegetables are cooked through.

Remove the beef from the pot and shred it into bite-sized pieces. Return the shredded beef to the soup.

Stir in the chopped cilantro and lime juice. Adjust seasoning with additional salt and pepper if needed.

Serve hot, garnished with avocado slices and accompanied by warm tortillas.