Sprinkle thyme on both sides of each halibut fillet and cook in hot oil over medium heat.
With a fork, test the fish to see if it flakes easily. This indicates that it is fried.
Transfer the fish to a warm plate.
Cook the garlic and onion in the same skillet until tender.
Pour the cornstarch mixture into the skillet after stirring the cornstarch into the stewed tomatoes.
Cook until the sauce has thickened.
Return the fish to the skillet and coat it with the sauce.