1. Preheat broiler to high. Combine egg whites, eggs, salt, pepper, and milk; stir with a whisk.
2. Heat a 9-inch cast-iron skillet over medium heat.
3. Layer in asparagus, shallots, and green onions.
4. Sprinkle with crumbled feta cheese.
5. Carefully pour egg mixture over cheese. Cook over medium heat 5 to 6 minutes or until eggs are partially set; then broil 5 inches from heat for 2 to 3 minutes or until browned and almost set.