Heat the oil in a soup pot over medium heat until shimmering. Add the onions and cook until translucent. Add the garlic and cook until fragrant. Add the meat and just brown on all sides. Add the pepper and cook until just softened.

Stir the tomato paste into the pot and cook for about a minute. Then add the tomatoes and heat through. Add the flour, stirring into the liquid, and cook for a couple minutes. Pour in the broth and season with salt, pepper, cumin, and chili powder. Bring everything to a boil, reduce the heat, and simmer covered on low for 2 hours, stirring occasionally. Add more broth or water as needed to keep it from getting too thick.

Once the meat is tender, remove from the heat. Serve warm with chopped fresh cilantro, warm tortillas, and sour cream, if desired.