1Heat oven to 425°F. In 4-quart saucepan, heat water, milk and butter to boiling. Stir in 2 pouches potatoes; beat with fork until smooth. Stir in 3/4 cup of the onions.
2Spread mixture in ungreased 2-quart baking dish. Sprinkle with cheese. Spread salsa over cheese. Top with olives and remaining onions.
3Bake uncovered 3 to 5 minutes or until onions are golden. Serve with sour cream and cilantro.