In a blender, combine the lemon juice, oil, soy sauce, parsley, onions, garlic, mustard and seasonings; cover and process until smooth. Pour 1 cup marinade into a 2-gal. resealable plastic bag; add turkey. Seal bag and turn to coat; refrigerate for up to 24 hours. Cover and refrigerate remaining marinade for basting.
Line the bottom of a large shallow roasting pan with foil. Drain and discard marinade; place turkey on a rack in prepared pan.
Bake, uncovered, at 325°F for 2 to 2-1/2 hours or until a meat thermometer reads 170°F, basting every 30 minutes with reserved marinade. (Cover loosely with foil if turkey browns too quickly.) Cover and let stand for 15 minutes before carving.