Preparation Prepare barbecue (medium-high heat). Whisk 2 tablespoons tarragon, 1 1/2 tablespoons oil and 1 teaspoon garlic in shallow dish to blend. Using rolling pin, lightly pound chicken between sheets of waxed paper to uniform 1/2-inch thickness. Sprinkle chicken with salt and pepper. Add chicken to tarragon mixture and turn to coat. Let stand 10 minutes. Meanwhile, blend tomato and remaining 1 tablespoon oil in processor until smooth. Add vinegar, remaining 1 tablespoon tarragon and remaining 1/4 teaspoon garlic and just mix in, using on/off turns. Season sauce to taste with salt and pepper. Grill chicken until brown and cooked through, about 4 minutes per side. Transfer chicken to plates. Spoon sauce around chicken. Garnish with tarragon sprigs, if desired, and serve.
Preparation Prepare barbecue (medium-high heat). Whisk 2 tablespoons tarragon, 1 1/2 tablespoons oil and 1 teaspoon garlic in shallow dish to blend. Using rolling pin, lightly pound chicken between sheets of waxed paper to uniform 1/2-inch thickness. Sprinkle chicken with salt and pepper. Add chicken to tarragon mixture and turn to coat. Let stand 10 minutes. Meanwhile, blend tomato and remaining 1 tablespoon oil in processor until smooth. Add vinegar, remaining 1 tablespoon tarragon and remaining 1/4 teaspoon garlic and just mix in, using on/off turns. Season sauce to taste with salt and pepper. Grill chicken until brown and cooked through, about 4 minutes per side. Transfer chicken to plates. Spoon sauce around chicken. Garnish with tarragon sprigs, if desired, and serve.