Drain & rinse kelp noodles: Open package, drain brine, rinse thoroughly under cold water for 20–30 seconds. Shake off excess water and, if desired, trim noodles into 6–8 inch lengths with kitchen shears for easy eating. Pat dry in a clean towel or salad spinner.
(Optional) Quick soak to soften: If you prefer a milder crunch, soak rinsed kelp noodles in 1 cup warm water with 1–2 tbsp apple cider vinegar or a squeeze of lime for 5–10 minutes. Drain and dry again.
Quick pickle the carrot (recommended): In a small bowl, whisk rice vinegar, sugar (or maple), salt, and warm water until dissolved. Add julienned carrot (and thinly sliced red onion if using) and let sit 5–10 minutes. Drain or reserve a tablespoon of pickling liquid to add to the salad for extra tang.
Prep remaining vegetables: Julienne red bell pepper and cucumber, shred red cabbage, slice scallions, and chop cilantro. Keep avocado separate until serving.
Make the dressing: Combine soy/tamari, rice vinegar, mirin/maple, sesame oil, neutral oil, grated ginger, minced garlic, lime juice, and red pepper flakes in a jar. Close and shake or whisk until emulsified. Taste and adjust: more lime for brightness, more maple for balance, or more chili for heat.
Toss salad: In a large bowl, combine drained kelp noodles, pickled carrot (drained), cucumber, bell pepper, cabbage, and scallions. Pour about three-quarters of the dressing over the mixture and toss gently to coat. Let the salad rest 5–10 minutes so the kelp noodles absorb flavor.
Finish & serve: Fold in cilantro and avocado (if using). Transfer to a serving platter or individual bowls, sprinkle toasted sesame seeds and reserved 1–2 tsp sesame on top, add optional protein if desired, and drizzle extra dressing at the table. Serve chilled or at room temperature.