In a large airtight plastic bag, combine the chicken breasts, garlic, lemon juice, Worcestershire sauce, parsley, salt, and pepper. Marinate the meat for 4 to 6 hours. Preheat the oven to 375°F. On a baking sheet, lay out the chicken breasts and brush two tablespoons of Dijon mustard. After 20 minutes of cooking, turn the breasts over and brush with two more tablespoons of Dijon mustard. Cook for an additional 20 minutes.