In a large saucepan place the butter, diced pepper and garlic and saute over medium heat for 3 minutes, until the butter is bubbling.
Add the oregano, cumin and paprika and saute for a further 3 minutes, until fragrant.
Add the tomato puree and chicken stock and bring to a simmer.
Add the pork carnitas, salt and pepper.
Allow to simmer for 2 minutes to ensure the pork is heated through.
Ladle the soup between three bowls and garnish with the shredded cheddar, diced avocado, cilantro and sour cream.