Place beans in a large saucepan and cover with water. Bring to a boil. Cook, uncovered, until beans are crisp-tender, 8-10 minutes; drain. In a large skillet, cook bacon and onion over medium heat until bacon is crisp and onion is tender, stirring occasionally, 3-5 minutes., Add beans to bacon mixture. Sprinkle with salt and pepper; toss to coat.