Combine beef and onion in a medium nonstick skillet over medium-high heat. Cook until beef is browned and onion is tender, stirring until meat crumbles.
Drain, if necessary, and return to skillet.
Add sloppy joe sauce to beef mixture, and bring to a boil. Reduce heat, and simmer 5 minutes, stirring occasionally.
While sauce cooks, cook frankfurters according to package directions.
Place 1 frankfurter in each bun. Spoon beef mixture evenly over frankfurters.
