In 12-inch nonstick skillet cook ground beef and onion until browned. Stir in Simply Potatoes and mushrooms. Spread into an even layer; press down lightly with spatula. Cook 6 to 7 minutes or until golden brown on the bottom.Drizzle with 1 tablespoon vegetable oil. Turn Simply Potatoes mixture over with spatula in sections. Continue cooking 6 to 8 minutes or until potatoes are golden brown and tender, turning again if necessary. Add tomatoes and salt. Cook until tomatoes are heated through. Sprinkle with cheese; cook until cheese is melted.