Prep: 10 minutes; Cook: 9 minutes; Other: 2 minutes
1. Preheat broiler.
2. Place mushrooms in a large ovenproof skillet. Cover mushrooms with cold water; let stand 2 minutes. Drain. Return mushrooms to skillet. Cover with cold water; bring to a boil. Drain. Pat mushrooms dry with a paper towel.
3. Combine egg whites and next 3 ingredients in a large bowl, stirring well with a whisk. Stir in mushrooms and cheese.
4. Heat oil in pan over medium-high heat. Add egg mixture; cook 3 minutes or until slightly set. Broil 3 minutes or until eggs are completely set and browned. Cut frittata into 4 wedges. Garnish with chives, if desired.