Cook pasta according to package directions. Drain. Preheat oven to 350°F.

In a 12-inch skillet, cook beef and onion until meat is brown. Drain fat. Stir in water and taco seasoning. Bring to a boil; reduce heat. Simmer uncovered for 2 minutes, stirring occasionally. Stir in cooked pasta, corn, olives, half of the cheese, salsa, and green chili peppers.

Transfer mixture to lightly greased 2-quart round casserole. Cover with aluminum foil and bake for 15 to 20 minutes until heated through. Sprinkle with remaining cheese and bake until melted.

Serve with shredded lettuce, tortilla chips, tomatoes, and sour cream, if desired.