Return the onions and garlic to the pan with the fish. Add the tomatoes, olives and thyme, sprinkling over and around the fish. Turn the heat to medium-low, cover the skillet with a tight-fitting lid and cook for about 3-4 minutes more, or until the fish is cooked and the onions are tender. Place a fillet on each plate, and spoon the onions, garlic and tomato mix over the fish, using all the juices that form in the pan. Sprinkle some fresh basil over each and serve immediately. 238 calories per serving; GL=1, Glycals=3