Thinly slice scallions, separating green and white parts. Sprinkle bluefish with 1 teaspoon of the salt, and set aside.
Heat 1 tablespoon of the oil in a large skillet over high. Add onion and lime wedges. Cook, without stirring, until onion and limes are nicely charred (they will look almost burned), 3 to 5 minutes. Remove from skillet, and set aside.
Heat remaining 2 tablespoons oil in skillet. Add carrots, almonds, ginger, garlic, and reserved white scallion slices. Cook, stirring often, until fragrant and just softened, about 6 minutes. Nestle fish pieces in carrot mixture. Top with mushrooms. Pour coconut milk over mixture. Sprinkle with remaining 1 teaspoon salt, and top with basil sprigs. Cover and reduce heat to low; cook 10 minutes.
Discard basil sprigs and ginger slices. Divide bluefish, vegetable mixture, and broth evenly among 4 bowls. Garnish with chile slices, reserved green scallion slices, and charred onion and lime wedges.