Cook green beans in boiling water to cover 5 to 10 minutes or to desired degree of doneness; drain and set aside.
Sauté onion and garlic in hot oil in a large skillet over medium-high heat 5 minutes or until onion is tender.
Add tomato sauce and sugar; cook, stirring often, 5 minutes. Add green beans, salt, pepper, and vinegar; cook 5 minutes. Sprinkle with parsley, and serve immediately.
* 1 pound frozen whole green beans may be substituted for fresh green beans. Cook according to package directions; drain well.