Preheat oven to 450°. Use tomatoes helat at room temperature until fully ripe. Cut tomatoes horizontally in halves, squeeze out seeds.
Place cut-side down in a well greased shallow 13x9 baking pan. Scatter onions and olives around tomatoes. Sprinkle with garlic, thyme,salt and pepper; drizzle with oliveoil. Roast until tomatoes are softened and wrinkled- 20-30 minutes.
Serve as side dish or or use in salsas,pizzas, pasta, rice etc.