Spray 8×8-inch glass baking dish with cooking spray.
Cook rotini as directed on package and drain.
While the pasta is cooking, melt butter over medium-high heat in a non-stick skillet. Cook mushrooms and onions in butter 6 to 8 minutes, stirring occasionally, until tender and browned.
Using the pot that the rotini was cooked in, mix cooked rotini, mushrooms, onions, diced turkey, cream of mushroom soup, sour cream, part of the parmesan cheese (save part to top casserole before baking), swiss cheese, salt and pepper.
Pour mixture into baking dish. Sprinkle with remaining parmesan cheese.
Bake 30 minutes or until bubbling on edges and completely heated through.
Let stand 5 minutes before serving. Sprinkle with parsley if desired.