1. Heat oil in a 5-quart Dutch oven and saute onion, cabbage, and celery until lightly browned or limp.
2. Add tomato sauce and tomato paste (if mixture seems too thick add a little water) and simmer over medium heat until vegetables are almost cooked, about 15 minutes, adding more water if necessary.
3. Add salt, pepper, and orzo and simmer, covered, until orzo is cooked, about 15 minutes. Remove from heat and sprinkle with cheese.
