Chop lotus root into half circles and add to a bowl with water, covering just over the top of the lotus root. Drizzle 2-3 tbsp of rice vinegar, stir together, and set aside.
Meanwhile, prepare chicken if using. Slice chicken into bite-sized pieces and sprinkle with garlic salt and pepper.
Chop ginger into small pieces and add to a wok over medium high heat with sesame oil and chicken. Cook until chicken is heated through.
Rinse and drain lotus root, then add to the wok with garlic, sugar, sake, soy sauce, mirin and arrowroot powder. Stir until sauce thickens and becomes sticky. Adjust taste to preference with soy sauce, sugar and/or mirin.
Add Napa cabbage and chicken, if using. Top with furikake before serving.