Pat the trout fillets dry with paper towels and marinate them with 1 tablespoon of the fish sauce and half of the black pepper for about 10 minutes.

In a deep skillet or traditional clay pot, heat the vegetable oil over medium heat and sprinkle in the sugar in an even layer.

Let the sugar melt and bubble without stirring until it turns a deep amber or mahogany color, watching closely to ensure it does not burn.

Immediately add the minced garlic, shallot, and ginger to the pan and stir quickly for about 30 seconds until fragrant, which stops the caramelization process.

Carefully place the trout fillets into the pan, turning them once to coat lightly in the caramel mixture.

Pour in the remaining fish sauce and the coconut water, bringing the liquid to a gentle boil.

Reduce the heat to low and simmer uncovered for about 20 minutes, basting the fish occasionally, until the sauce reduces to a thick, sticky glaze.

Add the sliced chilies during the last 5 minutes of cooking if you prefer a spicy kick.

Remove from heat and garnish generously with the remaining black pepper and sliced green onions before serving warm with steamed rice.