In small bowl whisk together cider vinegar, garlic, mustard, oregano, lemon juice and honey. Slowly drizzle in olive oil whisking constantly.
In medium saucepan bring chicken and olive oil to a boil. Stir in couscous. Cover and remove from heat. Let stand for five minutes and fluff with a fork. Allow to cool for 20 minutes.
In medium bowl combine couscous, red onion, kalamata olives, grape tomatoes, baby spinach, green olives and feta crumbles. Whisk vinaigrette one more time and drizzle over salad. Stir gently to combine. Add fresh ground black pepper to taste.