In a very large bowl, combine all the slaw ingredients: shredded green and red cabbage, carrots, red bell pepper, cucumber, green onions, and cilantro. Toss gently to mix.
In a separate medium bowl or jar, combine all the dressing ingredients: peanut butter, water, lime juice, tamari/soy sauce, maple syrup/agave, sesame oil, garlic, ginger, and red pepper flakes (if using). Whisk or shake vigorously until smooth and creamy. Add a little more water if needed to reach desired pouring consistency.
Pour about two-thirds of the dressing over the slaw mixture. Toss well until everything is evenly coated.
Let the coleslaw sit for 10-15 minutes at room temperature or in the fridge to allow the flavors to meld.
Before serving, add the chopped roasted peanuts and toss again gently. Taste and add more dressing if desired.
Serve immediately for maximum crunch, or chilled.