Combine the chicken and 2 tablespoons BBQ sauce in a plastic baggie and marinate for at least one hour. Preheat your grill and grill the chicken on both sides until cooked through. Finely chop the chicken and set aside to cool.
Combine the yogurt and ranch dressing mix in a medium bowl. Add the jicama, bell pepper, carrot, celery and chopped chicken.
Assemble the wraps: Lay out a piece of flatbread. Spread 1 tablespoon of BBQ sauce down the middle. Spoon half of the chicken mixture down the middle. Top with 1/3 cup of lettuce. Roll up tightly, and slice in half. Repeat with the remaining flatbread.