In a large skillet, cook beef over medium heat until no longer pink; drain and set aside. In the same skillet, saute' the onions, green pepper, celery and garlic in butter until crisp-tender. Stir in flour until blended. Return beef to the pan.
Cook, uncovered, over medium heat for 15 minutes, stirring occasionally.
Add cubed Mexican Velveeta, tomatoes, milk, and Cajun or Creole seasoning. Simmer, uncovered, for 15 minutes longer, stirring occasionally.
Add fettuccine; mix well.
Transfer mixture to a lightly greased 3-quart baking dish.
Sprinkle with Parmesan cheese.
Bake, uncovered, at 350º for 25 to 30 minutes or until heated through.