In 5- to 6-quart Dutch oven cook onion in hot oil over medium heat until tender, stirring occasionally. Add broth, water, beans, zucchini, carrots, and garlic. Bring to boiling. Add pasta and dried oregano, if using. Return to boiling; reduce heat. Simmer, covered, 5 minutes. Stir in Swiss chard. (If using spinach, stir in at the last with tomatoes.) Simmer, uncovered, 5 to 7 minutes more or until pasta is tender, stirring occasionally.
Stir in tomatoes and fresh oregano, if using. Remove from heat. Season with salt and black pepper. Sprinkle with additional fresh oregano.