For the dressing, combine the mayonnaise, sour cream, chili sauce, vinegar, onion salt, and pepper in a bowl and mix well. Chill, covered, in the refrigerator.
For the salad, peel and devein the shrimp. Combine the shrimp, rice, cucumbers, celery, and green onion in a bowl and mix well. Add the dressing and mix until coated. Chill, covered, for 2 hours or longer. Serve on a bed of lettuce.