Meanwhile, in a large salad bowl, toss lettuce with the remaining 1/4 cup vinaigrette. Spoon 1 1/2 cups lettuce into each of four shallow bowls. Top each with about 1/3 cup cucumber, 1/4 cup tomatoes, 3 tablespoons sweet pepper, and 2 tablespoons onion. Add chicken mixture to the center of each. Sprinkle with 2 tablespoons feta and 1 tablespoon olives. If desired, serve with lemon wedges.