In a large bowl, combine cucumber, mango, red bell pepper, red onion, and cilantro.
In a small bowl, whisk together lime juice, rice vinegar, maple syrup, soy sauce, and chili flakes (if using) to make the dressing.
Pour dressing over the salad and toss gently to coat evenly.
Sprinkle toasted peanuts on top for crunch before serving.
