In a large bowl, combine the cubed watermelon, cucumber, red bell pepper, red onion, cilantro, and mint. Gently toss to mix the ingredients evenly.
In a small bowl, whisk together the lime juice, fish sauce, honey, chili flakes, and a pinch of salt until well combined.
Pour the dressing over the salad and toss gently to coat all the ingredients.
Sprinkle the chopped roasted peanuts on top for added crunch.
Serve immediately or refrigerate for about 30 minutes to allow the flavors to meld before serving.