Cook the Korean udon noodles according to package instructions.
In a bowl, combine the sesame paste, soy sauce, grated ginger, minced garlic, rice wine vinegar, sesame oil, sugar, and sriracha.
Add 2 tbsp of the noodle cooking water to the sauce and mix well.
Drain the cooked noodles and add them to the sauce, tossing to coat evenly.
Season with salt and pepper to taste.
Garnish with scallions, sesame seeds, and chili flakes (if using).
