Preheat oven to 400 degrees . In small bowl, combine onion and vinegar. Let stand 15 minutes; drain. In large, ovenproof skillet, simmer pork, salsa, tomato sauce and broth, 3 minutes. Cover with chips, then cheese; bake until browned in spots, 10 minutes. Stir together sour cream, 5 tsp. water and pinch salt. Cut cheesy crust into quarters and transfer to plates. Top with onion, cilantro and sour cream.