Mix flour, garlic powder, salt and pepper together in a resealable plastic bag. Add cubed chicken to the bag and shake until well coated.
Heat the oil in a large frypan over medium heat. Add the chicken; cook and stir until the chicken is no longer pink, about 5 minutes. Stir in the capsicum, onion, zucchini, mushrooms, chicken stock and Italian dressing. Cover and simmer until vegetables and meat are tender, about 10 minutes.