In a large saucepan, heat oil over medium heat. Add onions and carrots; cook and stir until onions are tender, 4-6 minutes. Add potatoes and cook 2 minutes. Stir in water, tomatoes, broth and seasonings. Bring to a boil. Reduce heat; simmer, uncovered, until potatoes and carrots are tender, 8-10 minutes. , Add yellow squash and zucchini; cook until vegetables are tender, 8-10 minutes longer. Serve or, if desired, puree mixture in batches, adding additional broth until desired consistency is achieved.