Cut the acorn jelly into bite-sized pieces.
Julienne the cucumber, kimchi, and green onion.
Prepare cold naengmyeon broth or chilled water.
Place the acorn jelly, cucumber, kimchi, and green onion in a bowl.
Pour the cold broth over the ingredients.
Top with seaweed flakes and sesame seeds.
Add red pepper powder, vinegar, and mustard to taste.