01 - Preheat oven to 375°F. Grease a 9x13-inch baking dish.
02 - Boil salted water and cook pasta until just al dente. Drain and set aside.
03 - Melt butter in a large skillet over medium heat. Cook onions for 3 minutes. Add garlic and mushrooms; sauté until mushrooms soften and moisture evaporates, about 6 minutes.
04 - Sprinkle flour over vegetables and stir continuously for 1 minute. Slowly whisk in milk, broth, and wine if using. Simmer and stir until thickened, about 4–5 minutes.
05 - Add Parmesan, mozzarella, heavy cream, thyme, nutmeg, salt, and pepper. Stir until cheeses melt and sauce is smooth.
06 - Mix cooked turkey and peas if desired into the sauce. Gently fold in the drained pasta.
07 - Pour the combined mixture into the prepared dish, spreading evenly.
08 - In a small bowl, combine breadcrumbs, Parmesan, and melted butter. Sprinkle evenly over the pasta mixture.
09 - Bake uncovered for 25 to 30 minutes, until the top is bubbling and golden brown.
10 - Allow to rest for 5 minutes before garnishing with fresh parsley and serving.