Cook spaghetti according to package directions; drain. Meanwhile, in a large skillet, cook the beef, onion and garlic over medium heat until beef is no longer pink, 6-8 minutes, breaking up beef into crumbles; drain. Stir in the spaghetti sauce, salt and pepper; bring to a boil. Reduce heat; simmer, uncovered, for 20 minutes, stirring occasionally., In a small bowl, mix cream cheese and sour cream until blended; stir in green onions. In a greased 11x7-in. baking dish, layer the spaghetti, cream cheese mixture and meat mixture. Top with shredded cheese., Bake, covered, at 350° for 25 minutes. Uncover; bake until cheese is bubbly, 5-10 minutes longer.