In a small saucepan, combine the peanut oil, peanut butter, soy sauce, rice vinegar, chili paste, honey, garlic, and ginger. Heat over low heat, stirring until the peanut butter is melted and the mixture is well combined. Remove from heat and let cool slightly.

In a large bowl, combine the sliced cucumber, red bell pepper, and red onion. Pour the peanut chili oil over the vegetables and toss to coat evenly.

Let the salad sit for about 10 minutes to allow the flavors to meld.

Just before serving, sprinkle the chopped peanuts and cilantro (if using) over the salad. Toss gently and serve chilled or at room temperature.