Wash the lettuce thoroughly, shake off excess water, and tear by hand into bite-sized pieces or cut into three sections with a knife.
If there's too much moisture, the seasoning will taste bland, so let it rest in a strainer or dab with a kitchen towel.
For the sauce: In a small bowl, mix 2.5ml fish sauce, 7.5ml water, 5ml vinegar, 2g minced garlic, 2.5ml red pepper powder, 2.5ml sesame oil, and a little sesame seeds until well blended.
Pour the sauce over the lettuce and use your hands (not chopsticks) to gently toss and coat, shaking off any excess.
Lightly mix so the seasoning just coats the surface and the lettuce stays crisp and fresh without becoming watery.