In a large pot over medium-high heat, add the ground beef, breaking it apart as it cooks. Sauté for about 5-7 minutes, stirring occasionally, until browned and fully cooked. Drain any excess fat.

Add the diced onion and minced garlic to the pot with the beef. Sauté for 2-3 minutes until the onion is translucent and fragrant.

Stir in the taco seasoning and cook for another minute to allow the spices to bloom.

Pour in the diced tomatoes and chicken broth, scraping up any bits stuck to the pot. Bring to a simmer over medium heat and cook for about 10 minutes.

If using, mix in shredded chicken and cook for an additional 5 minutes until heated through.

Ladle the soup into bowls, top each serving with shredded cheese and fresh cilantro.