Heat the vegetable oil in a large pot or Dutch oven over medium-high heat.
Add the beef cubes to the pot and brown them on all sides, about 5-7 minutes. Remove beef and set aside.
In the same pot, add the chopped onion and bell pepper. Sauté for about 3-4 minutes until softened.
Stir in the minced garlic and cook for an additional minute until fragrant.
Return the browned beef to the pot, followed by the diced tomatoes, beef broth, ground cumin, dried oregano, salt, black pepper, and bay leaf. If using chili powder, add it as well.
Bring the mixture to a boil, then reduce the heat to low. Cover and simmer for 1.5 to 2 hours, or until the beef is tender.
Taste and adjust seasoning if needed. Remove the bay leaf before serving.
Serve hot, garnished with fresh cilantro, alongside rice or warm tortillas.