Season the fish with the salt and pepper.
Cut 4 pieces of aluminum foil large enough to wrap the fillets.
Brush one side of the foil with a little oil.
Place a fillet in the center of each piece; sprinkle with the onions, parsley, wine and remaining oil.
Bring the foil up over the top of the fish and double-fold the edges to make a tight package.
Bring the ends up and fold over.
Arrange the packages on a baking sheet.
Bake in a preheated 425° oven 25 minutes.
Carefully open one package and test fish with a fork; if it flakes easily, it is done.
If not, bake it a few more minutes.
Serve in the foil.