Start by grating the zucchini and squeezing out as much liquid as possible. In a bowl, mix ground chicken, zucchini, breadcrumbs, egg, lemon zest, and spices. Combine gently until everything is evenly blended.
Heat olive oil in a large skillet over medium heat. Form the mixture into evenly sized meatballs and place them in the pan. Cook until golden brown on all sides and nearly cooked through.
Remove the meatballs temporarily if needed and sauté onion and diced zucchini. Add couscous, mustard, parsley, and seasonings to the skillet. Pour in water, return meatballs, cover, and simmer until couscous is tender and fluffy.