Preheat oven to 350 degrees. Butter a 2 quart casserole dish.
Cook egg noodles according to package instructions. Reserve.
Sauté mushrooms and diced onion in 1 Tbl. butter until mushrooms have released their liquid. Remove from pan and reserve.
Melt 2 Tbl. butter in sauté pan over medium heat. Dust with flour and whisk until bubbly. Stir in milk and broth. Bring mixture to a boil, stirring continuously for 2-3 minutes. Remove from heat, stir in 1/4 cup Parmesan cheese. Season with salt & pepper to taste.
In a large bowl combine cooked noodles, mushroom/onion mixture, cream sauce, cubed turkey, green peas, and sliced olives. Pour into buttered casserole dish.
In a small bowl combine 1/4 cup Parmesan cheese, 1/4 cup cracker crumbs, and1 Tbl. melted butter. Sprinkle on top of casserole.
Bake for 30 minutes or until bubbly and top is golden.