Bring water to a boil, add shrimp, and cook 3 to 5 minutes.
Drain well, rinse with cold water.
Peel and devein shrimp.
Combine shrimp, celery, walnuts, and salad dressing, stir well.
To serve, line salad plates with leaf lettuce, and top each with a pineapple slice, mound shrimp mixture on pineapple slice.