Heat the oil in a large pot over medium heat until shimmering. Add the onions, bell pepper, chili powder, cumin, cayenne, and half the salt. Cook until vegetables are soft, about 7 minutes. Add garlic and cook for 30 more seconds.

Increase heat to medium-high and add the beef. Break it up with a spoon and cook until browned, about 10 minutes. Mix in the beans, tomatoes with juice, tomato puree, and remaining salt. Bring to a simmer, then lower the heat, cover, and cook for 45 minutes.

Uncover and simmer for another 45 minutes. Season with more salt and pepper to taste. Serve with optional garnishes like shredded cheese and sour cream.