Preheat oven to 350 degrees F. Spray a 9x13-inch baking dish with nonstick cooking spray; set aside.
Heat oil in a large pot over medium-high heat. Add onion, garlic and mushrooms and cook until onion and mushrooms are tender (about 3 minutes).
Add ground turkey, Italian seasoning, salt and pepper to the pot. Cook, breaking up meat, until turkey is cooked through. Sprinkle flour over the turkey mixture and mix to combine. Add chicken broth and stir to combine.
Break spaghetti noodles in half and add to the pot, and cook for 10 minutes or until pasta is al dente. Slowly pour in milk and mix well.
Pour turkey mixture into prepared pan and spread in an even layer. In a small bowl combine grated parmesan cheese, breadcrumbs and melted butter then sprinkle on top.
Bake for 20 minutes, or until cooked through and topping Is golden brown. Let sit for 5 minutes before serving.