Set your oven to 350 degrees Fahrenheit to start warming up.
Prepare the rotini noodles according to the package directions, then drain and keep them aside.
Fry the bacon pieces in a large skillet until they're crisp.
Take the bacon out and place it on paper towels to absorb excess grease.
Leave 3 tablespoons of bacon fat in the skillet and discard the rest.
Add the drained sauerkraut to the skillet with the reserved fat and stir to combine.
Put in the chopped onion, season with salt and pepper, and cook on medium heat, stirring now and then for about 10 minutes.
Transfer the cooked noodles into a 9x13-inch baking dish.
Crumble the cooked bacon and mix it in with the noodles.
Add the drained mushrooms and one can of cream of mushroom soup, stirring everything together well.
Incorporate the sauerkraut and onion mixture into the noodles and bacon blend, tossing to combine.
Spread the remaining can of cream of mushroom soup evenly over the top.
Place the dish uncovered in the oven and bake for around 45 minutes until bubbly and heated through.