Preheat oven to 350 degrees.
Add salt to a large pot of water and bring to a boil. Cook spaghetti al dente according to package directions. When pasta is almost done (cooked enough to eat but still pretty firm), grab about a cup of the pasta water and set aside. Drain the pasta and set aside.
While the pasta is cooking, melt butter in large pan, and cook mushrooms and onions over medium high heat until lightly browned and softened. Add garlic and cook an additional 3 minutes. Stir in flour and cook 3-4 minutes until golden and fragrant.
Deglaze the pan with the white wine, scraping the bottom of the pan. It will quickly evaporate.
Add broth and cream all at once. Cook until thick & bubbly. Bring to a gentle boil and then reduce heat to maintain a simmer so that it can thicken, stirring frequently. Add salt, pepper, and herbs.
Combine cooked spaghetti, turkey, peas, and about ¾ of the parmesan cheese with the mushroom sauce. Pour into a greased 9×13 pan or large dutch oven. The pasta will absorb a lot of the sauce when it cooks, so add some of the pasta water to thin it out, if needed.
Cover and bake 20 minutes. Sprinkle with parmesan and bake an additional 10-15 minutes, uncovered, until hot & bubbly.