Cook pasta according to package directions. Drain pasta; rinse with cold water. Drain again.
In a 12-inch skillet cook ground beef or turkey and onion until meat is brown. Drain fat. Stir in water and taco seasoning. Bring to boiling; reduce heat. Simmer, uncovered, for 2 minutes, stirring occasionally. Stir in cooked pasta, corn, olives, half of the shredded cheese, the salsa, and chilies.
Transfer mixture to a lightly greased 2-quart round casserole. Cover and bake in a 350 degree F oven for 15 to 20 minutes or until heated through. Sprinkle with remaining cheese.
Serve with shredded lettuce, tortilla chips, and tomato wedges. If desired, top with sour cream.