1. Preheat oven to 400ºF. Pat fish dry. Place each fillet on a large piece of heavy-duty foil. Mix salt, coriander and 1/2 tsp. cayenne; sprinkle over fish. Top with ginger and limes. Fold foil over fish; seal. Place on a baking sheet; roast until fish is cooked through, 12 to 18 minutes. Remove fish from foil; let cool. Discard limes and ginger; pat fillets dry. Flake fish with a fork.
2. Line a baking sheet with parchment. Mix egg whites, water chestnuts, cilantro, chives, shallots, lime juice, ponzu sauce and remaining 1/4 tsp. cayenne with fish. Fold in 1/2 cup plus 2 Tbsp. panko. Form 16 cakes, using 1/4 cup fish mixture for each. Put remaining panko in a shallow bowl. Dredge each cake in panko. Place cakes on baking sheet; chill for 30 minutes.
3. Warm 1 Tbsp. oil in a nonstick skillet over medium heat. Cook cakes in batches until golden, about 4 minutes per side. Wipe skillet between batches; add oil as needed.