Make broth by mixing 1 1/2 cups of water and naengmyeon broth soup base. Reserve 3 tablespoons for sauce; freeze the remainder until you have a slush-like consistency.
Cut watermelon in half and cut each end so the halves can sit up straight.
Remove some of the watermelon flesh to make room for the noodles.
Cook noodles according to package directions. Rinse under cold, running water. Drain completely.
Combine all sauce ingredients together in a bowl. Add noodles and mix together by hand.
Place noodles in the middle of the watermelon halves, and garnish with pickled radish, cucumber ribbons, hard-boiled egg and sesame seeds.
Place slush-like frozen naengmyeon broth around noodles, and add extra sauce if desired. Enjoy!