Cut tops off peppers and remove seeds. In a large kettle, cook peppers in boiling water for 3-5 minutes. Drain and rinse in cold water; set aside.
In a large bowl, combine the egg, 1/2 cup spaghetti sauce, onion, Italian seasoning, bread crumbs and 1/4 cup cheese. Crumble buffalo over mixture and mix well. Spoon into peppers. Place in a greased 3-qt. baking dish. Top with remaining spaghetti sauce.
Cover and bake at 350° for 55-60 minutes or until a thermometer reads 160°. Uncover; sprinkle with remaining cheese. Bake 5 minutes longer or until cheese is melted.