Remove the seeds and stems from the ancho chiles and tear them into pieces. Sweat the pieces in a hot dry pan over medium heat for one minute on each side. Put the pieces in a bowl and cover with hot water. Let soak for 30 minutes.

Place the whole, unpeeled garlic cloves in the hot pan and cook for about 10 minutes, until the peels darken in spots and the garlic becomes soft. Let cool and then peel the garlic.

Put the soaked chiles in the blender along with the garlic, raisins, black pepper, Mexican oregano, cinnamon, tamarind and 1 cup of the soaking water. Blend until smooth. Push the resultant paste through a fine mesh strainer.

Heat 1/4 cup of oil in a saucepan on medium heat. When the oil is hot, add the strained chile paste. Cook for 6 minutes, stirring constantly. Remove from heat, add the sugar and let cool.

Put the halibut in a resealable bag and add about half the cooled sauce. Seal the bag and let it marinate for at least an hour.

Put the halibut in a grill basket and cook over the grill for 2 minutes on each side. Add a little more sauce to the first side and cook one more minute.

Heat the remaining sauce and serve the fish with sauce on top.