Preheat oven to 375. Prepare a 2-quart casserole dish with cooking spray; set aside. In a skillet, heat oil over medium heat. Add potatoes, onions, and garlic. Cook ten minutes, or until potatoes are done. Remove from heat. Stir in sour cream, egg whites, and salt. Mix well. Place in prepared pan. Bake, uncovered, for 25 minutes, or until set. Top with cheese and bake for two minutes longer, or until cheese has melted.