Cook pasta according to package directions, adding the broccoli or cauliflower for the last 4 minutes of cooking. Drain.
Meanwhile, in a small bowl combine broth, lemon juice, honey, cornstarch, and white pepper; set aside.
In a large nonstick skillet stir-fry chicken in hot oil for 3 to 4 minutes or until no longer pink. Stir cornstarch mixture; add to skillet. Cook and stir until thickened and bubbly. Add carrot and tarragon; cook 1 minute more.
To serve, spoon chicken mixture over pasta. If desired, garnish with lemon slices. Serve immediately. Makes 4 servings.