Heat the remaining 2 teaspoons of oil in the same skillet. Add the carved chicken breast strips. Cook, stirring occasionally, until slightly browned on both sides, about 1 minute. Add the onion to the skillet. Cook until soft, stirring occasionally for approximately 3 minutes. Stir in the vegetables, hoisin sauce, garlic and soy sauce. Continue cooking with an occasional stir, until the vegetables begin to soften, about 5 minutes more.
TIP: If you prefer to use fresh vegetables, substitute frozen ingredients with 1 medium carrot peeled and diced small; 1 ear of corn, kernels removed from cob; 1/3 cup fresh peas and 1/3 cup stemmed and roughly chopped fresh green beans.