Position knife blade in food processor bowl; add first 9 ingredients. Process 1 minute or until blended.
Place chicken in a shallow baking dish; spoon 3 tablespoons cilantro mixture over chicken, turning to coat. Reserve remaining cilantro mixture. Cover and marinate chicken at least 4 hours, turning occasionally.
Coat grill rack with cooking spray; place on grill over medium-hot coals (350° to 400°). Place chicken on rack; grill, covered, 4 minutes on each side or until done.
Place a lettuce leaf on each of 2 bread slices. Place chicken breast halves on lettuce; spoon remaining cilantro mixture evenly over chicken, and top with remaining bread slices.