Cook pasta according to package directions. Drain; set aside.
Meanwhile, in a blender container or food processor bowl combine undrained tomatoes, tomato paste, tomato juice, sugar, dried oregano (if using), and pepper. Cover and blend or process until smooth. Set aside.
In a large skillet cook ground beef and onion over medium-high heat until meat is brown. Drain off fat. Stir in tomato mixture. Bring to boiling; reduce heat. Simmer, covered, for 10 minutes. Stir in pasta, fresh oregano (if using), and olives.
Divide the pasta mixture among six 10- to 12-ounce casseroles. Bake, covered, in a 375 degree F oven for 15 minutes. (Or, spoon all of the pasta mixture into a 2-quart casserole. Bake, covered, for 30 minutes.) Sprinkle with mozzarella cheese. Bake, uncovered, about 5 minutes more or until cheese is melted. Makes 6 servings.