Heat olive oil in a Dutch oven over medium-high heat.
Add onion and next 5 ingredients (onion through potatoes); cook 10 minutes, stirring occasionally.
Add the bell peppers, salt, and chickpeas; saute for 5 minutes. Stir in tomato and water. Bring to a boil; partially cover, reduce heat, and simmer for 25 minutes or until the potatoes are tender.
Remove vegetables with a slotted spoon. Set aside; keep warm. Reserve 1 cup of cooking liquid.
Bring reserved cooking liquid to a boil in a medium saucepan; stir in harissa, if desired. Gradually stir in couscous.
Remove from heat; cover and let stand for 5 minutes. Fluff with a fork.
Serve with vegetables; sprinkle with chopped parsley.