Heat oil in 10-inch skillet over medium heat. Cook garlic in oil 1 minute, stirring frequently.
Stir in reserved tomato liquid, chicken, onion, oregano, and pepper. Heat to boiling; reduce heat. Cover and simmer about 10 minutes, stirring occasionally, until chicken in no longer pink in center.
Stir in broth; heat to boiling. Stir in zucchini, couscous and tomatoes, breaking up tomatoes with a fork or snipping with kitchen scissors; remove from heat. Cover and let stand about 5 minutes or until couscous is tender and liquid is absorbed.