This slow-cooker version of our classic spaghetti casserole makes the dish easier than ever before. With the addition of ground round, onion, and spices, you'll find the result more flavorful than just dumping in a jar of sauce. But we still keep this satisfying recipe simple with just eight ingredients.
Cook ground round and onion in a large skillet, stirring until beef crumbles and is no longer pink; drain meat, and return to skillet.
Spoon half of meat mixture into a lightly greased 5-qt. slow cooker. Top with spaghetti. Spoon remaining half of meat mixture over top.
Combine pasta sauce, diced tomatoes, ½ cup water, and Italian seasoning. Pour mixture over meat, and sprinkle with Cheddar cheese.
Cover and cook on Low 4 hours. Let stand 10 minutes before serving. Serve with Parmesan cheese.