Recipes for “hamwiches” show up starting in the late 1950s. In the 1960s, they start appearing on school menus (sometime under their proper name of ham salad sandwiches) a sure sign of reaching “critical mass” in American culinary culture.
For a variation, consider one of the first recipes on the site, Portland, Oregon’s Spam Surprise Bun from 1967.
2 cups diced cooked ham
6 slices of cheese, diced
3 hard cooked eggs, diced
2 Tbsp. minced onion
1/4 cup mayonnaise
2 Tbsp. sweet pickle relish or chopped pickles
2 Tbsp. catsup or chili sauce
Combine all ingredients; spread on buttered buns. Place on cookie sheets and bake in 375 degree oven 12 to 15 min. Makes six sandwiches.