Scallions: Trim the roots and any bruised tops. Slice the scallions thinly on a bias. Add to a bowl of ice water and soak for ~10 minutes (this mellows out the pungency). Drain the scallions and pat dry.
Napa cabbage: Remove any wilted outer leaves. Slice in half lengthwise, then thinly slice crosswise, removing any bottom cores that are very tough. You should end up with ~ 16 oz / 450g sliced cabbage. Add the sliced leaves to a salad spinner bowl to rinse, then dry (or rinse in a bowl and dry well with towels).
Other veggies: For the cucumbers, either julienne or slice into half moons. For the carrots, use the large holes on a box grater to grate them (or a julienne peeler / food processor shredding disc). If using the bell pepper, slice thinly into strips.
In a serving bowl, combine the cabbage, cucumber, carrots, red pepper if using, and drained scallions. Toss to combine.
If using the optional edamame: If frozen, add to a bowl of hot water (or cook according to the bag instructions). Drain and pat dry, then toss edamame with a few pinches of salt.
Prep the Sesame-Garlic Dressing: In a small bowl, layer the following ingredients in this order: sesame seeds first, then chili flakes, ginger, and finally garlic on top.
Add the neutral oil to your smallest saucepan. Heat for 3 minutes on high or until shimmering (if you have a thermometer, wait until it registers 350ºF/175ºC).Immediately pour the hot oil over the garlic-ginger mixture. Allow to sizzle, then stir and rest for 1 minute. Stir the soy sauce, vinegar, agave, and sesame oil (if using) into the infused oil. Assemble: Sprinkle a pinch or two of salt into the cabbage salad and use your hands to toss. Fold in the seasoned edamame, if using. Pour the Sesame-Garlic Dressing on top and toss well until the veggies are well coated. Fold in the chopped peanuts. Taste and adjust the seasonings (I like to stir in ½ teaspoon soy sauce for savory saltiness and ½ teaspoon rice vinegar for tang).