BROWN meat in large skillet on medium-high heat; drain. Return to skillet.
ADD water, salsa and Macaroni; stir. Bring to boil; cover. Simmer on low heat 10 min. or until macaroni is tender, stirring occasionally. Add corn and Cheese Sauce Mix; stir. Cook and stir 2 min. or until heated through.
TOP with shredded cheese and onions.