Preheat grill to high. Brush tomatoes with oil and season with salt and pepper. Grill for 2 to 3 minutes or until the skins are lightly charred.
Place tomatoes and remaining ingredients, except tarragon, in a food processor and process until smooth. Add the tarragon and pulse a few times. Pour into a bowl and serve at room temperature. Garnish with additional tarragon, if desired.