Combine beef, water, half the onion, garlic, and 1 teaspoon salt. Simmer partially covered for about 2 hours until very tender.
Transfer beef to a plate. Strain and reserve 4 cups of broth, then shred the beef into irregular strands.
Make the Sauce:
Char tomatoes, bell pepper, and remaining onion in a dry skillet until softened and patchy brown. Blend with 2 cups reserved broth, cumin, cinnamon, cloves, and remaining salt.
Heat oil in the pot, add the blended sauce, and simmer 10 minutes.
Finish the Stew:
Add shredded beef, potatoes, and enough reserved broth to cover. Simmer 25 to 30 minutes until potatoes are tender and sauce coats the meat.
Stir in cilantro, adjust salt, and rest 10 minutes before serving.
Notes
Chuck roast gives enough connective tissue for tender strands and a flavorful broth.
Add broth gradually near the end; hilachas should be saucy but not thin.