Mix together soy sauce, lime juice, Worcestershire sauce, garlic and mustard. Reserve 1/4 cup marinade. Pour remainder over chicken in bag. Toss to coat well. Marinate in refrigerator 30 minutes or up to 4 hours. Drain chicken; discard leftover marinade. Sprinkle chicken with pepper.
Grill chicken by cooking over medium-high heat 5 to 6 minutes per side or until done.