Arrange a steamer basket or cake rack in a large wok or deep skillet and add enough water to reach just below the rack; set aside.

Place fish on a large piece of oiled parchment paper and season with salt.

Heat oil in a small skillet over medium-high heat.

Add ginger, green onions and chiles and cook, stirring frequently, until fragrant but not browned, about 1 minute.

Stir in lime zest and fish sauce and cook for about 10 seconds more.

Pour mixture over fish and wrap up parchment paper snugly to form a packet.

Carefully transfer fish to rack in wok or skillet.

Bring water to a simmer over medium heat, cover and steam until fish is just cooked through, 8 to 10 minutes.

Carefully remove parchment packet from wok and transfer to a large plate.

Serve with lime wedges.