How to Make It
In a small skillet, heat 1/4 inch of oil until shimmering. Add the ginger matchsticks and fry over moderate heat, stirring, until browned and crisp, about 2 minutes. Using a slotted spoon, transfer the fried ginger to paper towels to drain.
In a small saucepan, combine the granulated sugar with 1 tablespoon of water. Cook over moderate heat until a deep amber caramel forms, 3 to 4 minutes. Whisk in another 2 tablespoons of water and cook over low heat until the caramel is dissolved, 1 minute. Add the fish sauce, palm sugar, black pepper and 3/4 cup of the coconut water and simmer over moderate heat until the caramel sauce is reduced to 1/2 cup, 3 to 5 minutes.
In a large enameled cast-iron casserole, heat the 2 tablespoons of oil until shimmering. Add the ginger rounds, shallots, chiles and garlic and stir-fry over moderately high heat until the shallots are golden, about 3 minutes. Add the caramel sauce and scallions and simmer until the sauce is reduced by half, 3 to 5 minutes. Nestle the catfish fillets in the sauce and cook over moderately high heat, turning once, until caramelized and cooked through, about 6 minutes. Using a spatula, transfer the catfish fillets to a serving platter.
Add the remaining 1/4 cup of coconut water to the casserole and cook over low heat, scraping up any browned bits from the bottom, until the sauce is hot, about 3 minutes. Spoon the caramel sauce over the catfish. Scatter the fried ginger matchsticks and cilantro over the fish and serve with steamed rice.