Combine eggplant, peppers, onion, tomatoes with juices, chickpeas, garlic, oil, basil, oregano, salt, and pepper in a 6-quart slow cooker.
Cover; cook on low 5 hours until eggplant is mostly tender.
Stir in zucchini. Cover; cook on low 1 1/2 to 2 hours more until vegetables are tender but intact. Stir in vinegar.
Boil 1 1/4 cups water in a small saucepan. Stir in couscous, cover, remove from heat, and rest 10 minutes.
Fluff couscous with a fork; divide among 6 shallow bowls.
Spoon ratatouille and chickpeas over couscous, adding a little tomato cooking liquid to each serving.