Step 1Cut the grilled vegetables into 1-inch pieces. Toss vegetables, mozzarella and basil together in bowl. Set aside.
Step 2Heat oil in 10-inch nonstick skillet over medium heat. Combine eggs and 3 tablespoons Parmesan and pour into skillet. Cook eggs 1 minute, then add vegetable mixture and salt and pepper to taste. Cook until bottom of frittata is golden and set but top is still wet, about 10 minutes.
Step 3Wrap skillet handle in foil. Sprinkle remaining cheese on top of frittata, then broil frittata until top is set and slightly brown, 3 to 5 minutes. Invert frittata onto serving plate, cut into wedges and serve.