To make soup: Chop tomatoes and toss with salt. Drain in colander over bowl for 15 minutes. Set tomato liquid aside and add tomatoes to food processor puree with vinegar, sugar, and lemon juice until smooth. Pour puree through a sieve into a bowl, pressing hard on solids. Discard solids. Stir in tomato liquid for desired consistency and salt and pepper, to taste. Soup may be made 1 day ahead and chilled, covered. Season soup again before serving.
Stir tarragon into soup and thinly slice cherry tomatoes. Serve soup sprinkled with tomatoes, zucchini, and onion.
Recipe courtesy of Gourmet Magazine