In a large bowl, combine the shredded cabbage, grated carrots, sliced red bell pepper, sliced cucumber, chopped shrimp or chicken (if using), chopped cilantro, and sliced green onions. Toss gently to mix the ingredients evenly.
In a separate small bowl, whisk together the peanut butter, soy sauce, rice vinegar, honey, and sesame oil until smooth. If the dressing is too thick, add water one tablespoon at a time until you reach your desired consistency.
Drizzle the creamy peanut dressing over the salad and toss until everything is well coated.
Serve immediately or chill in the refrigerator for about 30 minutes to let the flavors meld before serving.