Mix oil, garlic, salt and pepper; coat chicken breasts with oil mixture. Place in hotel pan, cover and refrigerate at least 30 minutes or up to 24 hours.
For each serving, to order: Grill 1 chicken breast until juices run clear. Slice across the grain. In bowl, toss chicken with 2 ounces watercress and 3 tablespoons dressing. Plate watercress mixture. Top with 2 ounces tomato wedges, 1 1/2 ounces onion slices and 3/4 ounce mushroom slices.
To make Bacon Dressing: In large skillet over medium heat, cook bacon until crisp. Drain all but 1 cup fat. Add oil, onions and garlic to skillet. Cook about 5 minutes or until onions are tender. Add vinegar, soy sauce, basil, sugar and pepper. Bring to simmer and simmer for 2 minutes. Season with salt. Cover and keep warm; whisk before using. (Yield: about 5 cups)