Slice the pork roast into 1 inch thick slices - makes 6 to 10 slices. Lay the slices on a deep roasting pan sprayed with cooking spray or rubbed with olive oil. Sprinkle meat with meat tenderizer and garlic salt. Place it, uncovered in the oven about 45 minutes, turning it halfway through cooking,until just cooked.
While the pork is cooking, remove the sauerkraut from the jars and drain out the juice. You don't have to squeeze it, just let it drain. Place the drained sauerkraut in a large bowl. Dice the onion and add it to the sauerkraut. Shred the apple and add it to the sauerkraut also. (You can process both in a food processor to make it easy, just don't over process. Mix the sauerkraut, apple and onion until combined and set it aside.
Cut the kielbassa into two to three inch pieces and place them in the pan with the cooked pork. There will be juices in there, don't drain the pork - the juice will flavor it. Then spread the sauerkraut over the pork and kielbassa. Pour the beer over the sauerkraut, sausage and pork mixture, then drizzle the barbecue sauce over the top. Cover the pan with a lid or place a cookie sheet on top to cover it. If you use aluminum foil the sauerkraut and barbecue sauce will cause it to pit and disintegrate, and you don't want that in your food. Bake at 350 for three hours or until pork is fork tender. Serve with mashed potatoes.
