For sauce, in a small bowl stir together yogurt, mustard, and tarragon. Set aside.
Spray a wok or large skillet with nonstick spray coating. Heat over medium-high heat. Stir-fry carrot and garlic 1 minute. Add zucchini; stir-fry about 3 minutes more or until vegetables are crisp-tender. Remove from wok.
Add oil to hot wok. Stir-fry chicken for 3 to 4 minutes or until no longer pink. Return vegetables to wok. Add sauce to wok; toss to coat all ingredients with sauce. Cook and stir for 1 minute or until heated through.
If desired, serve with hot cooked noodles. Makes 4 servings.