Using a meat mallet, flatten pork chops between sheets of waxed paper to a thickness of about 1/4 inch. Season both sides of chops with pepper. In a large nonstick skillet heat butter over medium heat. Cook chops for 4-5 minutes, turning once, until nicely browned. Remove chops; keep warm. Add green onions to skillet; cook and stir for 30 seconds. Stir in chicken broth and mustard. Cook, uncovered, for 5 minutes, stirring occasionally. Stir in maple syrup and balsamic vinegar. Continue cooking, uncovered, until sauce thickens slightly. Return chops to skillet; heat through. Spoon sauce over chops to serve.