If halibut is not available, use cod or red snapper.
To test fish for doneness, place a fork in the thickest part and gently twist. The fish will flake easily when done.
You can make your own foil packet by placing food on half of an 18x12-inch piece of heavy-duty aluminum foil. Fold other half of foil so edges meet. Seal edges, making a tight 1/2-inch fold; fold again. Allow space on sides for heat circulation and expansion.