COOK spaghetti in large saucepan as directed on package, omitting salt.
MEANWHILE, heat dressing in large nonstick skillet on medium heat. Add broccoli and peppers; stir-fry 3 min. or until crisp-tender. Add meat and hoisin sauce; stir-fry 2 to 3 min. or until meat is done.
DRAIN spaghetti; return to pan. Add broth; cook 1 min. or until heated through, stirring occasionally. Add meat mixture and onions; mix lightly.