1. Heat oil over medium heat in large nonstick ovenproof pan. Saute potato, ham and onion (not green onion yet) until potato is just tender.
2. Meanwhile, whisk eggs, egg whites and baking powder until frothy and baking powder has dissolved. Add green onion to pan. Gently pour egg mixture into pan, covering the ham and veggie ingredients. Sprinkle cheese over top.
3. Place pan, uncovered, in 375F preheated oven. Cook until egg has set, about 25 minutes.