In a large bowl, combine onions, cider vinegar, sugar, caraway seeds, and salt. Add the shredded cabbage and toss to coat. Set aside.

Slice the corned beef lengthwise, then cut each slice into 3-inch pieces.

Place half the corned beef on the bottom of the pressure cooker. Top with half of the shredded cabbage. Add the rest of corned beef on top of the cabbage and sprinkle the pickling spice over the meat. Finally, add the rest of the cabbage and its juice. Pour the beef stock and water into the cooker and lock the lid in place.

Pressure on HIGH for 40 minutes.

While corned beef and cabbage are cooking, cut out a well in the center of each roll and set the rolls aside on cookie sheet. Crumble the tops and insides of the rolls into coarse breadcrumbs. Melt the butter in a skillet over medium heat and add the breadcrumbs, cooking for a few minutes or until the breadcrumbs are lightly browned and toasted. Set the toasted crumbs aside.

When the time on the pressure cooker is almost up, pre-heat the oven to 350ºF.

Release the pressure using the QUICK-RELEASE method and carefully remove the lid. Sprinkle half of the Swiss cheese into the cooker stir a few times and let the cheese melt into the hot liquid. With a slotted spoon, fill the wells of the rolls with the corned beef and cabbage mixture. Top with some thousand island dressing and divide the remaining Swiss cheese over each roll. Sprinkle the toasted breadcrumbs on top of the cheese.

Place in a 350º F oven for about 8 minutes until the cheese is melted and bread is warm and crispy. Serve immediately.