Pour the chicken stock and water into a saucepan. Stir in the garlic then bring to a boil. Stir in the couscous, cover the pan then remove from heat. Allow the couscous to stand until all the water has been absorbed, about 5 minutes; fluff with a fork. Allow the couscous to cool to warm temperature.
In a large serving bowl, lightly toss the couscous, sundried tomatoes, olives, feta cheese and chickpeas. Mix the oregano, black pepper, white wine vinegar and lemon juice in a small bowl then pour over the couscous mixture. Toss again to serve.