Divide the salad ingredients among 4 quart-sized (32-ounce) jars, layering in the following order: 2-3 tablespoons of dressing in the bottom of each jar, followed by the onions, cucumbers, olives, tomatoes, chicken, and lettuce. Screw on lids and keep chilled until ready to serve. For easy eating, pour into bowls to serve.
Optional: Bring a separate container of feta cheese with you on your picnic and sprinkle on the salads before eating, if desired.