For the lettuce, wash, drain and dry. Cut into 1-inch thick strips. Transfer to a large mixing bowl. Toss in onion and green onion.
In a small bowl, combine all dressing ingredients. Whisk until sugar has dissolved.
When ready to serve, pour half of the dressing over. Toss and adjust with more dressing if needed. Sprinkle with sesame seeds. Serve immediately.
If you like spicy food, add more gochugaru.
Gochugaru can be bought from Korean supermarket or from Amazon. There are different spicy levels. For hot and spicy, look for “maewoon gochugaru”. For milder one, look for “deolmaewoon gochugaru”. For more tips about picking gochugaru, read here.
Gochugaru can be stored in the freezer to keep fresh for a long time.