Coat large dutch oven with oil. Place over medium-high heat until hot. Add onion and garlic; saute 5 minutes or until tender. Add water and next 9 ingredients; bring to a boil. Cover, reduce heat, and simmer 20 minutes. Add orzo, and cook, uncovered, over medium heat for an additional 10 minutes, or until orzo is tender. Ladle soup into individual bowls, and sprinkle with mozzarella shreds.