Lightly oil a 9-by-13-inch roasting pan; set aside.
In a small bowl, mix oregano, coriander, 1 1/2 teaspoons salt, and 1/2 teaspoon pepper. Rub mixture evenly over pork tenderloins.
Place pork in prepared pan.
Roast pork 5 minutes; brush with 1/3 cup of Balsamic Nectar, coating entirely. Roast another 5 minutes; brush with remaining 1/3 cup of Balsamic Nectar. Continue roasting until internal temperature registers 155 degrees on an instant-read thermometer, about 10 minutes more.
Remove from pan. Let rest 10 minutes; slice 1/4 inch thick.
Spread mustard over split rolls, add lettuce leaf, and then layer half with pork and onions. Top with remaining halves of rolls.