In a large stockpot add oil and heat to medium high. Add the chopped onions and sauté for a couple of minutes. Add the carrots and celery and sauté until quite soft about 8 minutes.
Add diced tomatoes, oregano, and tomato paste. Cook for a few minutes.
Add the ¼ cup of the fresh chopped basil and cook for a couple of minutes.
Working in batches, puree the mixture until smooth and return to pot. If you prefer your soup not as blended, you don’t have to puree all the soup.
Add the chicken or vegetable broth and bring to a slow boil and cook for several minutes until the soup begins to slowly boil. If the soup is too thick for your liking, add ½ cup more of broth.
Optional – If you like a velvety texture, turn the heat off the pot and add ¼ cup of heavy cream.
Season to taste with sea salt and pepper.
Garnish with the remaining chopped basil leaves and serve.