In a large skillet, cook beef and onion over medium heat until meat is no longer pink; crumble meat; drain. Stir in the pasta, contents of seasoning packet, salsa, water, chili powder, salt and cayenne., Bring to a boil. Reduce heat; cover and simmer until pasta is tender, about 15 minutes, adding more water if necessary. Stir in tomatoes; sprinkle with olives and cheese. Cover and simmer until heated through, 3-4 minutes. Serve with sour cream if desired.