Step 1

Light a grill and line the grate with lightly oiled heavy-duty aluminum foil. Arrange the banana leaves in two stacks of 3 and sprinkle each with one-fourth of the ginger and scallion whites. Cut 3 gashes into the flesh on both sides of each fish, cutting to the bone. Set the fish on the banana leaves and scatter the remaining ginger and scallion whites on top. Sprinkle with the sherry and soy sauce. Fold the leaves over the fish and tie each packet in 3 places with kitchen string.

Step 2

Place the packets on the grate, close the grill and cook over high heat for 25 minutes, turning the packets once, until a thermometer inserted in the thickest part of the fish registers 140°. Carefully transfer the packets to a platter and let rest for 2 minutes. Cut them open and peel back the banana leaves.

Step 3

Meanwhile, in a skillet, heat the oil. Add the garlic and chiles and cook over low heat, stirring, until the garlic is crisp, 2 minutes. Spoon the oil, garlic and chiles over the fish; season with salt. Scatter the cilantro and scallion greens on top and serve with lime wedges.