Heat oil in a large frying pan over moderate heat and add chicken and cook, turning for 3 minutes or until browned all over.
Remove from pan and add onion to pan and cook and stir for 3 minutes or until soft and then add tomato and 1 cup boiling water and mix well.
Add chicken and bring to a simmer, cover, cook stirring occasionally for 15 minutes.
Add zucchini and cook for 5 minutes or until chicken is cooked.
Meanwhile place couscous and stock powder in a medium heatproof bowl and stir in 1 cup boiling water, cover with plastic food wrap, set aside for 5 minutes or until liquid is absorbed and then using a fork, fluff and separate grains.
Combine parsley and zest in a small bowl and then add half the parsley mix to the couscous and toss to combine.
Spoon chicken and sauce over couscous and serve sprinkled with remaining parsley mix.