Separate the cabbage into leaves. Lay out one leaf and slice it horizontally through the white stem to make it narrower. Repeat with the remaining leaves, then stack and cut them crosswise into ⅛-inch / 3 millimeter shreds. Place in a colander with the cucumber and toss with the salt.
Meanwhile, bring a large pot of water to a boil. Add the vermicelli and cook according to the package instructions. (If there are no instructions, cook till tender but still a little chewy, which can be anywhere from 25 seconds to 10 minutes, depending on the brand and the thickness.) Rinse under cold water and drain. Use kitchen shears to snip the noodles into shorter, more manageable lengths.
Squeeze out the excess liquid from the cabbage and cucumber by pressing them between your hands. Drop each squeezed handful into a large bowl, without rinsing the vegetables. Add the vermicelli noodles, carrot, scallion, garlic, soy sauce, vinegar, sugar, MSG and sesame oil and stir well. Taste and adjust seasoning. You can enjoy this immediately or chill it in the refrigerator, covered, for a few hours to let the flavors meld. Stir in the cilantro just before serving for the freshest flavor.
