1Beat eggs, cheese, Italian seasoning, salt and pepper until well blended; set aside.
2Melt butter in ovenproof 12-inch nonstick skillet over medium heat. Cook mushrooms, bell pepper, onion and olives in butter about 2 minutes, stirring occasionally, until vegetables are crisp-tender. Spread mixture evenly in bottom of skillet.
3Pour egg mixture evenly over vegetable mixture; reduce heat to medium-low. Cover and cook 9 to 11 minutes or until eggs are set in center and light brown on bottom. Remove cover.
4Set oven control to broil. Broil frittata with top about 5 inches from heat about 2 minutes or until golden brown. Cut into wedges.