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.
Test Kitchen Tips
A Monterey, California, businessman named David Jacks made Monterey Jack cheese popular in the late 1800s by shipping it to San Francisco and other areas of the U.S.
To keep pasta from sticking together when cooking, use a large pot with plenty of water. Add a little cooking oil if desired (this also prevents boiling over).