Cook pasta in a large pot of boiling water until al dente; drain.
In a large skillet, cook ground beef and onion over medium heat until brown; drain.
Mix in tomato soup, diced tomatoes and taco seasoning mix.
Stir in pasta.
Spoon beef mixture into a 9x13 inch baking dish. Sprinkle crumbled taco chips and grated cheese on top.
Bake for 30-35 minutes, until the cheese is melted.
Serve with chopped green onions and sour cream, if desired.