Heat oil in a large skillet over medium-high heat; add the chicken and cover. Cook until chicken is browned, turning once about 15 minutes. Remove chicken; slice, set aside. Heat butter in a medium-low heat, stir in flour, salt and mustard. Add the milk. Mix yolks, lemon peel and juice in a bowl. Stir in one third of egg mixture into sauce pan. Gradually stir in remaining egg mixture. Bring to a gentle boil, stirring continually. Remove pan from heat and stir in parsley and sour cream. Cook pasta according to package directions, and drain. Toss with oil and stir 3/4 c. of sauce and feta into pasta. Top with sliced chicken and remaining sauce. Sprinkle with dill and more feta if desired.