Cook pasta according to package directions; rinse with cold water. Drain.
Process tomato sauce and diced tomatoes in a blender 20 seconds or until smooth. Set aside.
Cook ground beef in large skillet over medium-high heat, stirring until meat crumbles and is no longer pink. Stir in dried Italian seasoning, salt, pepper, fennel seed, cream cheese, ricotta cheese, and 2 cups mozzarella cheese. Spoon into manicotti shells; arrange stuffed shells in lightly greased 13- x 9-inch baking dish.
Pour tomato mixture over shells; sprinkle with remaining 2 cups mozzarella cheese.
Bake at 350° for 20 minutes or until cheese is melted and bubbly. Let casserole stand 10 minutes before serving. Sprinkle top with chopped fresh parsley, if desired.
Note: Casserole may be assembled and frozen up to 1 month. Thaw in the refrigerator overnight; bake, covered, at 350° for 30 minutes. Uncover and bake 15 more minutes or until cheese is melted and bubbly. If you prefer a smaller casserole, use 2 (11- x 7-inch) baking dishes. Proceed as directed.