Rub salt into fish; set aside.
In a glass or ceramic baking dish, combine ginger, lime juice, sugar, scallions, and cilantro; mix well. Add fish; turn to coat. Cover fish and marinate in refrigerator for 20–30 minutes.
Preheat broiler to high. (If desired, line a broiler pan with aluminum foil for easy clean up.)
Remove fish from marinade and place on broiler pan; brush with marinade. Broil for 6 minutes; flip fish and brush with marinade again. Cook until fish is no longer translucent in middle, about 5–7 minutes more depending on thickness of fish. Remove fish immediately; cut into 8 large pieces.
Divide fish, lettuce and salsa among tortillas; fold in half and serve with lime. Yields 2 tacos per serving.