Whisk the dressing ingredients. Place the chicken in a large, resealable plastic bag and pour in 1 cup of the dressing. Press the air out of the bag and seal tightly. Turn the bag to distribute the dressing, place in a bowl, and refrigerate for 4 to 6 hours, turning occasionally. Cover and refrigerate the remaining dressing.

Prepare the grill for direct cooking over medium heat (350° to 450°F) .

Prepare the grill for cooking over medium heat (400°F) .

Remove the chicken from the bag, shaking off and discarding the excess dressing. Grill the chicken, smooth (skin) side down first, over direct medium heat, with the lid closed, until the meat is firm to the touch and opaque all the way to the center, 8 to 12 minutes, turning once or twice. Remove from the grill and let rest for 3 to 5 minutes. Cut the chicken into chunks.

Lightly brush the romaine halves on both sides with oil and grill over direct medium heat, with the lid closed, until slightly wilted, about 2 minutes, turning once. Remove from the grill.

Lightly brush the romaine halves on both sides with oil and grill over medium heat, with the lid closed, until slightly wilted, about 2 minutes, turning once. Remove from the grill.

Serve the romaine warm with the chicken, dressing, tomatoes, and parsley. Season with salt and pepper.