Step 1

In a 12-inch skillet, combine the sugar and 2 tablespoons of the coconut water. Cook over medium-high, occasionally swirling the pan to help the sugar dissolve and to encourage even browning, until the caramel is mahogany in color and smokes lightly, 4 to 6 minutes.

Step 2

Remove the pan from the heat and add the fish sauce along with the remaining 2 tablespoons coconut water; the mixture will bubble vigorously and the caramel will harden in spots. Bring to a simmer over medium and cook, stirring, until the hardened bits have dissolved. Add the chilies, lemon grass, ginger and pepper, then cook, stirring, until fragrant, about 30 seconds. Increase to medium-high and stir in the chicken. Bring to a simmer and cook, stirring occasionally, until the sauce reduces and clings to the chicken, 10 to 14 minutes.

Step 3

Remove from the heat, then discard the lemongrass. Stir in the lime juice. Transfer to a serving dish and sprinkle with the scallions.