Preheat oven to broiler. Position oven rack 4 to 6 inches from heat source.
Brush onion with oil. Arrange tomatoes and onion in broiler pan. Broil, turning frequently, until tomato skins blister and onion softens, about 20 minutes. Let tomatoes cool about 5 minutes. Remove skin and core.
Cut each tomato crosswise in half; remove seeds. In food processor puree tomatoes and onion until smooth.
In saucepan over high heat combine tomato-onion mixture, broth, thyme, orange zest, salt and pepper. Bring to a simmer and heat through. Serve warm or chilled. Makes 4 servings. Enjoy!