Prep the aromatics: thinly slice the shallots, mince the garlic, slice the chilies, and cut the scallions into 1-inch pieces. Rinse the catfish steaks briefly and pat very dry.
Set a clay pot (tแป) or heavy saucepan over medium heat. Add the neutral oil, then sprinkle in the sugar in an even layer. Cook undisturbed until the sugar melts and turns a deep amber, 3โ5 minutes; swirl gently if needed.
Carefully pour in the coconut water to stop the caramel (it will sputter). Stir to dissolve any hardened caramel.
Add the shallots, garlic, fish sauce, and chilies to the pot. Stir and bring to a steady simmer, 1โ2 minutes.
Nestle the catfish steaks into the sauce in a single layer. Spoon some sauce over the top, reduce to a gentle simmer, cover partially, and cook for 10 minutes.
Uncover, turn the fish carefully, and continue simmering until the fish is just cooked through and the sauce reduces to a glossy syrup that thickly coats a spoon, 10โ15 minutes.
Sprinkle in the black pepper and add the scallions. Simmer 1 minute to soften the scallions, then remove from heat. Let rest 2โ3 minutes and serve hot with steamed rice, spooning the syrupy sauce over the fish.