In a large pot, heat the vegetable oil over medium-high heat. Add the beef flank steak and brown on all sides.
Remove the beef from the pot and set aside.
In the same pot, add the chopped onion, red bell pepper, and green bell pepper. Cook until the vegetables are softened, about 5 minutes.
Stir in the minced garlic and cook for another minute.
Add the tomato sauce, beef broth, and white wine (if using). Stir to combine.
Return the browned beef flank steak to the pot. Add the ground cumin, paprika, dried oregano, black pepper, and salt.
Bring to a boil, then reduce the heat to low. Cover and simmer for 2-3 hours, or until the beef is tender and easily shreds with a fork.
Once the beef is cooked, remove it from the pot and shred it using two forks. Return the shredded beef to the pot.
Stir in the sliced green olives and capers. Simmer for an additional 10 minutes to allow the flavors to meld.
Garnish with chopped fresh cilantro before serving.
Enjoy your meal!