Cook spaghetti according to package directions. Meanwhile, in a Dutch oven, saute onions in 6 tablespoons butter until tender. Add mushrooms and red pepper; saute 4-5 minutes longer or until vegetables are tender. , Stir in flour and salt until blended. Gradually whisk in milk and bouillon. Bring to a boil; cook and stir for 2 minutes or until thickened. Stir in turkey and cheese; heat through. Remove from the heat. , Drain spaghetti; add to turkey mixture and mix well. Transfer to one greased 13x9-in. baking dish and one greased 11x7-in. baking dish. , Melt remaining butter; toss with bread crumbs. Sprinkle over casseroles. Bake, uncovered, at 350° for 30-35 minutes or until heated through. Sprinkle with parsley.