Luncheon Chicken Salad

1/2 cup finely chopped onion

2 celery ribs , finely chopped

1/3 cup finely chopped English cucumber

1 large tart apple , finely chopped

1 1/4-1 1/2 cups low-fat mayonnaise

1/2 cup light sour cream

1/4-1/2 teaspoon salt , to taste

1/4 teaspoon pepper

1/8 teaspoon curry powder

1/2 teaspoon cilantro

1/2 teaspoon parsley

3 dozen wheat dinner rolls, split

lettuce leaf