Season the beef cubes generously with salt, black pepper, cumin, chili powder, and garlic powder. Set a heavy pot over high heat and let the oil get hot until it shimmers.

Brown the beef in batches in the hot oil in the heavy pot over high heat—do not crowd—then remove and set aside. Brown on each side until darkly seared, about 3–5 minutes total per batch, and ensure the bottom stays sizzling.

In the same pot, sauté the diced onion and green bell pepper for 5 minutes. Cook until softened and slightly translucent, adjusting heat so it stays at a steady sizzle.

Add the minced garlic and cook 1 more minute. Stir constantly until fragrant but not browned, about 30–60 seconds, with visible golden edges.

Sprinkle the flour over the vegetables and stir for 1 minute. Keep stirring until the flour smells toasted and forms a thick coating.

Add the beef broth and diced tomatoes, scraping up the browned bits from the bottom of the pot. Stir until the gravy looks smooth and medium-brown, no dry flour streaks.

Return the browned beef to the pot and add the oregano. Cover and simmer on low for 1.5–2 hours, until the beef is extremely tender and the gravy has thickened to a spoon-coating consistency.

Ladle the carne guisada into warm bowls and serve with warm flour tortillas, fresh cilantro, and lime. The beef should look glossy in the dark gravy, with tortillas that steam when filled.