Wash the cucumbers thoroughly. Cut them in half lengthwise and then slice them into half-moons about ¼ inch thick.
In a large mixing bowl, combine the sliced cucumbers, red onion, and diced red bell pepper.
In a separate small bowl, whisk together the lime juice, fish sauce (or soy sauce), sugar, red chili flakes, and salt until the sugar has dissolved.
Pour the dressing over the cucumber mixture and toss well to ensure everything is evenly coated.
Add the chopped cilantro and mint to the salad, gently mixing them in to avoid bruising the herbs.
Taste and adjust seasoning if necessary; you can add more fish sauce, lime juice, or chili flakes according to your preference.
Let the salad sit for about 5 minutes before serving to allow the flavors to meld together. Serve chilled or at room temperature.
Consider topping the salad with grilled shrimp or tofu for added protein, if desired.