1. Cook bacon and onion in a Dutch oven over medium heat, stirring often, 6 to 8 minutes or until browned. Transfer bacon mixture to a plate, reserving drippings in Dutch oven.
2. Cook beans in hot drippings, stirring often, 8 to 10 minutes or to desired degree of tenderness. Stir in vinegar, sugar, and bacon mixture. Cook, stirring often, 3 minutes or until thoroughly heated. Season with salt and pepper to taste.