In a large pot over medium heat, add the olive oil. To the pot, add the onion and garlic and cook for 5 minutes, until tender.
To the onion mixture, add the next 7 ingredients (chicken broth through mushrooms) and stir. Cover soup and reduce heat to low. Simmer for 25 minutes, until chicken is cooked through and vegetables are tender.
Using a large soup-spoon, spoon soup into bowls and top with basil. Serve warm.