Olive oil, for roasting pan
1 teaspoon dried oregano, crumbled
3/4 teaspoon ground coriander
Coarse salt and ground pepper
2 pork tenderloins (3/4 pound each)
2/3 cup balsamic vinegar
2 tablespoons light-brown sugar
4 teaspoons Dijon mustard
8 country rolls, or other small rolls, split
1 large red onion, sliced into thin rounds
Preheat oven to 450 degrees. 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.
In a small saucepan, bring vinegar and brown sugar to a boil over high heat; cook, stirring occasionally, until mixture is reduced to 1/2 cup, about 3 minutes. Remove from heat.
Roast pork 5 minutes; brush with 1/3 of balsamic mixture, coating entirely. Roast another 5 minutes; brush with remaining balsamic mixture. 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, then layer half with pork and onions. Top with remaining bread halves.