Meanwhile, make the braised red onions: Cook the bacon in a large saucepan until it renders and begins to crisp. Pour off half the fat. Add the red onions to the pan along with the wine, soy sauce, thyme, brown sugar and vinegar. Cook over medium heat, stirring occasionally, until all the liquid boils away and the onions are tender, about 15 minutes. The onions can be refrigerated until you are ready to bake the fish.