Preheat oven to 350 degrees F.

Cook the spaghetti in a large pot of boiling, salted water to just al dente (should still have a good “bite” to it). Drain and set aside.

Meanwhile, in a large pot, melt 3 tablespoons of butter over medium low heat. Add onions and garlic and cook until onions are tender, about 3-4 minutes. Add mushrooms and cook until tender; another 3-4 minutes.

Sprinkle flour over the onions and mushrooms and whisk together until coated. Cook until golden; 1-2 minutes. Add the chicken broth and whisk together until smooth. Bring to a simmer and continue cooking until the mixture thickens; 2-3 minutes. Season with salt and pepper. **If sauce seems too thick, add a little milk or broth.

Stir in sour cream, 1 1/2 cups of grated mozzarella cheese and 1/2 cup grated Parmesan cheese until cheese is melted, then stir in the cooked spaghetti, turkey, peas and olives.

Pour the casserole into an 11x7-inch baking dish. Sprinkle the remaining ½ cup of Mozzarella on top of the spaghetti.

Mix together breadcrumbs with 3 tablespoons melted butter and sprinkle evenly over the casserole.

Bake in the preheated oven for about 20-25 minutes or until golden and bubbly.

Let stand for 10 minutes before serving.

Garnish with fresh minced parsley.