BRUSH both sides of fish lightly with oil. Set wire rack on baking sheet and place fish on top.
Broil about 2 to 3 inches from heat for 5 minutes. Turn over and continue broiling until just opaque in center, 6 to 8 minutes longer.
BEAT egg white until stiff, in medium bowl with electric mixer. Fold in cheese, mustard and green onions. Spread mixture over top of fish.
Return to broiler until topping is golden, about 1½ minutes longer.