For the treacle sauce I just chopped an onion and 4 cloves garlic. Cook the onion about 7 minutes in some oil. Add garlic and cook 1 minute. Add about half the tin of treacle, and an equal amount of cider vinegar. Add a tablespoon or so of chopped oregano. Simmer about 5 minute, blend smooth, then simmer to thicken stirring occasionally for about 45 minutes.

Then just grill the fish glazing with the treacle mixture as it cooks.