Put 1 tbsp. of Lee Kum Kee Hoisin Sauce on 1 slice of bread. Repeat with 1 tbsp. on a second slice of bread.
Build one sandwich by placing 2 slices of ham, ¼ cup cheese, 2 tbsp. scallions on one of the slices of bread with Lee Kum Kee Hoisin Sauce. Repeat with 2 more slices of ham, ¼ cup of cheese, 2 tbsp. scallions on the remaining slice of bread with Lee Kum Kee Hoisin Sauce.
Heat a pan over medium heat. Add ½ tbsp. of butter to the pan. Spread 1 tbsp. of mayonnaise on the outside of the first sandwich. Repeat for the second sandwich.
Place the mayo side down in the pan with butter. Put an additional tablespoon of mayonnaise on each slice of bread that is facing up. Toast the sandwich on each side until it’s golden and the cheese is melted.