1tablespoonred pepper flakesuse Korean chili flakes if you can find them: gochugaru
5scallionstrimmed and thinly sliced (white and green parts)
¼cupminced red onion
Toasted sesame seedsfor garnish, optional
Slice the watermelon rind into 2-inch or so pieces, then use a vegetable peeler to scrape the rind into super thin slices. Don't worry about evenly sized pieces. Place the thin watermelon slices into a colander and sprinkle with the salt. Toss well, and let sit in the sink to drain for about 30 minutes.
Meanwhile, place the fish sauce, sugar, garlic, ginger, and kochujang paste in a food processor and process to combine. Turn the mixture into a large bowl and stir in the chili flakes, scallions, and red onion.
Rinse the watermelon rind with cold water, then squeeze it in handfuls to remove excess water. Spread out the watermelon rind on a clean, dry dishtowel. Roll up the dishtowel with the rind in it, and squeeze it out over the sink to remove as much water as possible. Unroll the dishtowel and add the watermelon rind to the marinade. Toss to combine.
Transfer the kimchi to a clean jar, cover, refrigerate, and let marinate for at least 24 hours before serving. Top with the sesame seeds if desired.