Whisk together orange juice, chicken broth, soy sauce, cornstarch, sugar, hot mustard and red-pepper flakes in small bowl.
Heat oil in large skillet over high heat. Add chicken thighs; cook 4 minutes or until no longer pink. Remove with slotted spoon to plate.
Reduce heat to medium-high. Add celery to skillet; cook 1 minute. Add squash, zucchini and water; cook, stirring, until vegetables are softened, about 6 minutes.
Add the chicken strips and the cut up sweet red pepper to the skillet; cook for 2 minutes. Add the orange sauce from the bowl, stirring to combine; cook until the sauce is slightly thickened, about another 2 minutes.
Serve with the hot cooked couscous, if desired. Makes 4 servings.
