In 5-quart Dutch oven, cook bacon over medium heat 10 to 12 minutes, stirring occasionally, until crisp.
Using slotted spoon, transfer to small bowl.
Increase heat to medium-high. Add beef and onions to bacon drippings in Dutch oven; cook 9 to 11 minutes, stirring frequently, until beef is browned and onion is softened. Drain; transfer to medium bowl.
Return Dutch oven to medium heat. Add quinoa and salt; cook over medium heat 1 to 2 minutes, stirring occasionally, until fragrant. Slowly stir in broth. Stir in beef mixture. Heat to simmering over high heat, stirring occasionally.
Cover; reduce heat to medium-low. Cook 23 to 27 minutes or until liquid is absorbed and quinoa is tender. Stir in spinach.