Season chicken with salt, pepper and lemon juice. Cook on the grill for about 5 minutes on each side. Remove from the grill and let it rest 1-2 minutes. Slice chicken into strips 1/4 inch thick.
Lay one slice Flatout bread on a chopping board. Spread barbecue sauce over bread. On one side, add chicken, onion, cilantro, scallion and cheese. Fold the other side over it.
Please on the grill for about 2 minutes on each side or until the cheese has melted and the bread is slightly crispy.