Divide halibut into 4 pieces. Brush with olive oil and season with salt and pepper to taste.
On a baking sheet, place fish in parchment cooking bag or on a large sheet of parchment paper. Scatter green onions and capers over fish. Close bag tightly or wrap up parchment.
Bake for 15-20 minutes. Fish is done when you can see liquid bubbling in the cooking bag and the parchment is very lightly browned.