Place the beef chunks in a large pot and cover with the water or beef broth. Bring to a boil, reduce heat to low, cover, and simmer for about 1.5 to 2 hours until the meat is very tender.

Remove the beef from the pot and let it cool slightly. Reserve 1 cup of the cooking liquid. Once cool enough to handle, shred the beef into thin strands using two forks or your fingers.

In a large skillet or deep pan, heat the vegetable oil over medium heat.

Add the chopped onion and red bell pepper to the skillet. Sauté for 5-7 minutes until the vegetables are soft and the onions are translucent.

Stir in the minced garlic, ground cumin, and paprika, cooking for another minute until fragrant.

Add the shredded beef to the skillet and stir to combine with the vegetables.

Pour in the crushed tomatoes, Worcestershire sauce, and the reserved 1 cup of beef cooking liquid. Mix well.

Simmer uncovered over medium-low heat for 15-20 minutes, stirring occasionally, until the sauce thickens and coats the meat richly. Season with salt and pepper to taste.

Garnish with fresh chopped cilantro if desired and serve hot.