Cook spaghetti according to package directions; drain., In a large nonstick skillet, heat oil over medium-high heat. Add broccoli, bok choy and carrots; stir-fry 4 minutes. Stir in 1/4 cup broth, 1 tablespoon soy sauce and pepper; reduce heat to medium. Cook, covered, 3-5 minutes or until vegetables are crisp-tender. Stir in green onions; remove from pan., In same skillet, mix hoisin sauce and the remaining broth and soy sauce; add meatballs. Cook, covered, over medium-low heat 4-5 minutes or until heated through, stirring occasionally., Add bean sprouts, spaghetti and broccoli mixture; heat through, tossing to combine. Top with additional green onions.