I added celery and vegetable broth also, and a 14 oz can of diced tomatoes. (epicurious.com)
Plus you can easily double the recipe by sending in a larger 28 - ounce can of diced tomatoes, and simply doubling up on all the other ingredients. (topsecretrecipes.com)
I added one large can of diced tomatoes as well as a pinch of coriander and cumin because I was craving more veggies in the soup. (paleopot.com)