Place the halibut steaks in one layer in a skillet with a lid.
Add all the other ingredients except the onion& butter.
Bring to a boil covered reduce heat and cook 1 minute.
Strain off 1 cup of liquid, put the lid back on the skillet, remove from heat source and allow the fish to finish cooking 5-10 minutes depending on the thickness of the halibut (the steam inside the skillet will be enough to finish cooking the fish).
Meanwhile bring the cup of liquid to a boil, reduce heat and cook uncovered until the liquid is reduced to apprx 1/3 cup, add the onions& whisk in the butter.
Remove the halibut from the skillet (it should be opaque and flake easily when touched with a fork).