In a large Dutch oven or soup pot, heat the olive oil over medium-high heat. Add the ground beef and cook, breaking it up with a spoon, until fully browned. Drain any excess grease.

Add the chopped onion to the pot with the browned beef. Cook for 5-7 minutes, or until the onion is softened and translucent. Stir in the minced garlic and cook for another minute until fragrant.

Stir in the diced tomatoes (undrained), diced green chilies (undrained), beef broth, and water. Add the chili powder, ground cumin, smoked paprika, cayenne pepper (if using), salt, and black pepper. Stir well to combine all ingredients.

Bring the soup to a gentle simmer. Reduce the heat to low, cover the pot, and let it simmer for at least 15-20 minutes, allowing the flavors to meld. Stir occasionally.

While the soup simmers, in a small bowl, whisk together the softened cream cheese and lime juice until smooth and lump-free.

Remove the soup from the heat. Gradually whisk small amounts of the hot soup into the cream cheese mixture, tempering it, then slowly add the cream cheese mixture back into the main soup pot, stirring constantly until fully incorporated and creamy. Do not bring back to a boil after adding cream cheese, as it may curdle.

Ladle the hot Zesty Keto Taco Soup into bowls. Garnish each serving with a dollop of sour cream, diced avocado, shredded cheddar cheese, and fresh chopped cilantro. Serve immediately.