Cut chicken into 1/2-inch square pieces. Combine 1 Tbsp. each cornstarch and teriyaki sauce with garlic; stir in chicken. Let stand 30 minutes.

Meanwhile, combine 4 teaspoons cornstarch, remaining 4 Tbsp. teriyaki sauce, ketchup and 1 cup water.

Cut zucchini in half lengthwise, then diagonally into 1-inch pieces.

Cook noodles according to package directions; keep warm.

Heat 1 Tbs. oil in wok or large skillet over high heat. Add chicken and stir-fry 2 minutes; remove.

Heat remaining oil in same pan. Add zucchini and onion and stir-fry 4 minutes, or until tender-crisp. Add chicken, teriyaki sauce mixture and tomatoes. Cook and stir until mixture boils and thickens. Pour over hot noodles; toss to combine before serving.