3 Tbsp chopped fresh tarragon (or 1 Tbsp dried tarragon)
3 Tbsp olive oil
1 1/4 teaspoons minced garlic
4 boneless chicken breast halves, skin on (about 1 1/2 pounds)
2 cups chopped fresh tomato (1-2 tomatoes, depending on their size)
2 teaspoons balsamic vinegar
Salt and pepper to taste
1 Get the grill started on medium high heat. While the grill is heating up, whisk together half of the tarragon, half of the oil, and all but 1/4 teaspoon of the minced garlic in a shallow dish. 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.
2 Meanwhile, in a blender or food processor, blend the tomato and remaining olive oil until smooth. Add the vinegar and remaining tarragon and garlic and pulse until well mixed. Season to taste with salt and pepper.
3 Grill chicken until brown and cooked through, about 4 minutes per side. Transfer chicken to plates. Spoon sauce around chicken.