1. Cook pasta according to package directions; drain. Return pasta to saucepan.
2. Meanwhile, for sauce, in a medium saucepan heat the cheese and milk over low heat until cheese melts, whisking until smooth. Stir in lemon peel and lemon juice. Stir in zucchini and salmon; heat through. Pour sauce over pasta; toss to coat.
3. Transfer to a warm serving platter. Sprinkle with chives.