Melt butter in a 10 inch skillet over medium heat. Sprinkle chicken with salt and pepper. Cook chicken in butter 15 to 20 minutes, turning once until juice is no longer pink. Remove chicken from skillet and keep warm.
Mix water and gravy mix in small bowl; pour into same skillet. Stir in frozen veggies and mushrooms. Heat to boiling; reduce heat. Simmer uncovered about 5 minutes, stirring occasionally, until largest pieces of potatoes are hot. Add chicken;cover and simmer about 2 minutes or until chicken is heated through.
Serve vegetables and gravy mixture over chicken. Sprinkle with the chives or parsley if desired.