Prepare the dressing - In a small mixing bowl, whisk together the finely chopped lemongrass, lime juice, fish sauce, brown sugar, and red pepper flakes until the sugar has dissolved. Set aside. - If you don't have a whisk, you can also shake the ingredients in a jar with a tight-fitting lid. Taste the dressing and adjust the seasoning according to your preference - you can add more lime juice for tanginess or more sugar for sweetness. Be careful not to touch your eyes or nose after handling the lemongrass, as it can cause irritation.

Prepare the watermelon and onion - Cube the watermelon into bite-sized pieces and thinly slice the red onion. Place them in a large mixing bowl. - For an extra fancy presentation, you can use a melon baller to scoop the watermelon into balls instead of cubes. If you're sensitive to the pungency of raw onion, you can soak the sliced onion in cold water for a few minutes to mellow the flavor.

Chop the herbs and nuts - Chop the mint leaves and peanuts into small pieces. Add them to the mixing bowl with the watermelon and onion. - To release the oils in the peanuts and intensify their flavor, you can crush them using a mortar and pestle. If you don't have peanuts, you can use other nuts like cashews or chopped almonds. You can also adjust the amount of herbs and nuts according to your taste.

Assemble the salad - Drizzle the dressing over the watermelon mixture and toss gently until everything is well coated. Serve immediately. - To prevent the watermelon from becoming too watery, don't pour the dressing too long before serving. You can also reserve some of the dressing on the side for people who want extra, or drizzle it over individual servings instead of the whole salad. For an added crunch, you can sprinkle some more chopped nuts on top of the salad before serving.