Wash the lettuce leaves thoroughly and look for any wilted parts or tiny worms. Rinse and then dry them. Place them on the cutting board and cut into small bite sized pieces using the knife. Place them in the large salad bowl.
Now slice the white parts of the green onions lengthwise into long thin strips. Mostly they will curl up because you have slice them real thin. Add these onion slices to the salad bowl and toss together with the lettuce leaves.
Make the dressing in a small bowl. Whisk together the soy sauce, water, white sugar, vinegar, sesame oil, and red pepper flakes.
Right before serving, pour the dressing over the lettuce leaves and onion and toss together well so that it is coated over the vegetables. Do not store for long before serving because the dressing might cause the lettuce leaves to lose their freshness.