Cook spaghetti al dente, 8-10 minutes, or according to package directions. When pasta reaches al dente, drain and do not rinse.
Meanwhile, in a large skillet or pot, on medium heat, melt butter. Add onion, garlic, and mushrooms and cook for about 5 minutes, until onion is soft.
Add flour and cook for one minute while stirring.
Add broth and cream and whisk (or stir) until thickened and bubbling. Boil for 1 minute then stir in cream cheese until melted. Add parsley, Italian dressing mix, salt, and pepper.
Combine sauce with cooked spaghetti, turkey, 1 cup mozzarella, and ¼ cup parmesan. Add spaghetti mixture to baking pan and top with remaining mozzarella cheese.
Cover and bake 20 minutes. Sprinkle with remaining parmesan and bake uncovered for an additional 10-15 minutes, or until bubbling.