Remove skin from tuna and place between 2 sheets of plastic wrap. Flatten with a tenderizer utensil until tender but not completely flattened, 1/4 to 1/8 inch.
Roll tuna tightly and place in freezer for 4 hours until firm.
Remove plastic wrap and slice tuna into fine slices. Lay on plates.
Stir remaining ingredients together. Pour mixture over tuna. Season 20 minutes before serving.
Serve with lemon wedges.
Serves 2 as an entrée or 4 as an appetizer.