How to Make It
Light a grill and oil the grates. Using a sharp knife, cut 3 shallow slits on each side of the fish and brush with fish sauce; grill over moderate heat, turning once, until white throughout and the skin is crisp, 17 to 20 minutes. Transfer the fish to a baking sheet and let cool.
Meanwhile, in a small bowl, whisk the lime juice with the palm sugar, chile powder and the 3 tablespoons of fish sauce.
Remove the skin and meat from the catfish; discard the bones. Pinch the meat into small pieces and transfer to a bowl. Chop the skin into small pieces and add to the bowl with the shallots, scallions and chopped cilantro, mint and dill. Add the lime dressing and toss well. Transfer the salad to a platter and sprinkle with roasted rice powder. Serve with vegetables, herbs and lime wedges and pass any remaining roasted rice powder at the table.
You can substitute 1 pound skin-on catfish or wild salmon fillets for the whole fish; adjust the grilling time.
Roasted rice powder is available at Asian markets, but it can be made at home: In a skillet, toast 1/4 cup raw sticky rice over moderate heat, stirring until golden, 12 minutes; transfer to a spice grinder and let cool, then grind to a powder. Store in an airtight container for up to 2 months.