How to Make It
In a bowl, combine the lemongrass, oil and a pinch each of salt and pepper. Add the chicken and turn to coat. Let marinate at room temperature for 30 minutes.
Light a grill and oil the grates. Grill the chicken over moderately high heat, turning once, until cooked through and lightly charred, about 6 minutes. Let cool slightly, then cut into 1/2-inch dice.
In a mini food processor, combine the chiles, garlic, brown sugar, lime juice, fish sauce and water and pulse until the chiles and garlic are finely chopped. Pour the dressing over the chicken. Stir in the watermelon, cilantro and mint.
Spoon the salad into Chinese soup spoons and serve.
Variation Slice the chicken. Slice the watermelon and stamp out rounds. Arrange the watermelon in shallow bowls and top with the chicken, dressing, cilantro and mint.