Prepare the relish: In a small saucepan, bring the thinly sliced red onion and water to a boil over medium heat.

Cook for 1 minute, stirring frequently, then drain the water.

Transfer the drained onion to a bowl.

Add the chopped roasted sweet red peppers, cider vinegar, halved garlic cloves, dried oregano, salt, pepper, and ground cumin to the bowl.

Let the relish stand at room temperature for 1 hour.

Remove and discard the garlic cloves.

Cover the relish and place it in the refrigerator.

Make the sandwiches: Mash together the minced garlic, ground cumin, and salt.

Rub the garlic mixture over the pork tenderloin.

Place the tenderloin in a shallow baking pan.

Bake uncovered at 425 degrees for 30-35 minutes, or until a meat thermometer reads 160 degrees.

Allow the cooked pork tenderloin to stand for 10 minutes before slicing it thinly.

Heat the olive oil in a large skillet over medium heat.

Top four slices of sourdough bread with sliced pork, the desired amount of relish, and 2 slices of Swiss cheese.

Top with the remaining bread slices to form sandwiches.

Cook the sandwiches for 2 to 4 minutes on each side, or until golden brown and the cheese is melted.