Arrange mackerel in single layer in shallow baking dish.
Combine egg and oil in electric blender; process until thick.
Add lemon juice, vinegar, salt, Worces- tershire sauce, hot sauce, fish garni and pepper.
Pro- cess until mixed; pour over mackerel.
Let stand for 30 minutes.
Arrange onion over mackerel.
Bake at 400 degrees for 25 minutes.