Place green beans in a small saucepan and cover with water. Bring to a boil; cook, uncovered, for 8-10 minutes or until crisp-tender., Meanwhile, in a small skillet, cook bacon over medium heat until crisp. Using a slotted spoon, remove to paper towels. Drain, reserving 2 teaspoons drippings; saute onion in the drippings until tender. Stir in brown sugar and vinegar; heat through. Drain beans and place in a bowl; stir in onion mixture. Top with bacon.