In a large skillet, cook beef and onion over medium heat until no longer pink.
Add garlic; cook 1 minute longer. Drain.
Stir in spaghetti sauce, diced tomatoes, mushrooms and Italian seasoning. Season with salt & pepper.
Bring to a boil. Reduce heat; simmer, uncovered, 20 minutes.
Preheat oven to 350°.
Cook pasta according to package directions; drain.
Add to beef mixture and gently stir in sliced plum tomatoes.
Transfer to an ungreased 13x9-in. baking dish. Sprinkle with cheeses.
Bake 25-30 minutes or until bubbly and heated through.
