Heat a pan with oil.

Slice the onion and add to pan. Sautee onions on medium heat five to 10 minutes until translucent.

Add the rest of the ingredients, besides fish, and bring to a boil.

Then add fish slices, bring to a boil and cook on low heat for 45 minutes.

When cooled, remove the fish from the pan.

Strain the sauce and discard the onions.

Pour the sauce over the fish, covering the slices. Serve chilled.