In a large skillet, heat oil. Add onion, green pepper and salt.
Cook until tender, drain oil.
In a small bowl, combine ketchup and vinegar, mix well.
Add to skillet.
In a small bowl, combine reserved pineapple syrup and cornstarch, mix well.
Add to skillet and cook for 3-5 minutes, or until mixture thickens.
Stir in pineapple chunks, or crushed pineapple, and simmer for 3 minutes.
Add meatballs and cook until heated through.
Put into a serving bowl, garnish with green onions, and serve.