Place the drained green beans, drained black olives cut in half, the cubed Feta cheese, the cherry tomato halves and sliced red onion in a bowl. Add the whole bottle of Italian dressing to the bowl. Toss the ingredients gently to coat them. Place the salad in the refrigerator for at least 4 hours and up to overnight before serving. Toss the salad ingredients together with a large spoon right before serving.