Bring a large pot of lightly salted water to a boil.
Add pasta and cook for 8 to 10 minutes or until al dente; drain. Preheat oven to 350 degrees F (175 degrees C).
Place bacon in a large, deep skillet. Cook over medium high heat until evenly brown. Stir in onions, and cook until translucent. In a separate pan, saute the mushrooms in butter.
In a large bowl, combine pasta, bacon, onion, mushrooms, sauerkraut and condensed soup. Season with salt and pepper.