Slice tops off capsicums to make lids. Scoop out seeds and membranes; discard. Simmer the capsicums and lids in a large saucepan of lightly salted boiling water, covered, for 5 minutes. Drain and set aside.
Preheat oven to 180°C. Heat oil in a medium saucepan over medium heat. Add zucchini and garlic. Sauté 2 minutes. Stir in juice. Cook 1 minute and remove from heat. Stir in the couscous, chickpeas, tomato, oregano, salt, pepper and fetta.
Fill each capsicum with couscous mixture. Place upright in a shallow baking dish. Cover with capsicum lids. Bake just until filling is heated through, about 20 minutes.