Heat butter. Add onions and cook about 10 minutes. Add flour and stir until blended. Slowly add stock and stir over low heat, until thick and smooth. Season to taste. Add turkey, tomatoes and cheese. Arrange turkey mixture and spaghetti in layer in greased casserole. Top with bread crumbs. Bake for 25 minutes at 350 degrees.
Makes 4-6 servings