Cook onion and garlic in oil in a 5 quart Dutch oven
until tender. Stir in tomato, thyme, and wine. Bring to a boil. Add mussels and reduce
heat to a simmer
, covered, about 5 minutes or until mussels open. Discard unopened mussels. Divide mussels among 4 serving bowls. Spoon juices over mussels.