Set your oven to 350 degrees Fahrenheit to warm up.
Prepare the rotini according to package directions, then drain and put aside.
Fry the bacon in a large skillet until crispy, then transfer it to paper towels to drain.
Drain excess bacon grease from the skillet, leaving about 3 tablespoons in the pan.
Add the drained sauerkraut to the skillet and stir it into the bacon grease.
Mix in the chopped onion, season with salt and pepper, and cook over medium heat for around 10 minutes, stirring now and then.
Put the cooked rotini in a 9x13 inch baking dish.
Crumble the cooked bacon over the pasta and mix it together
Add the sliced mushrooms and one can of cream of mushroom soup, stirring to combine.
Pour in the sauerkraut mixture and gently toss everything.
Spread the remaining can of mushroom soup evenly on top.
Bake in the oven uncovered for approximately 45 minutes until heated through and bubbly.