1. Arrange oven racks on lower and center third position of oven. Heat oven to 425 degrees F. Line the bottoms of a broiler pan and a jelly-roll pan with foil. Brush pans with 1 teaspoon oil.
2. Arrange sweet peppers and garlic on one pan and zucchini and onion on the other. Brush vegetables with 1 tablespoon oil. Roast zucchini and onion on lower rack and sweet peppers and garlic on center rack 15 minutes. Remove zucchini and onion from oven. Transfer bell peppers to lower rack; roast 10 minutes more, until charred. Remove vegetables from oven and let stand 5 minutes. Remove garlic from skins. Coarsely chop garlic and vegetables. Transfer to a bowl. Stir in 1/2 teaspoon of the salt and the parsley. Reduce oven temperature to 350 degrees F.
3. Brush a 9-inch nonstick round cake pan with remaining 1/2 teaspoon oil. Whisk eggs, remaining 1/2 teaspoon salt and the ground red pepper in a bowl. Stir in vegetables and Parmesan. Pour mixture into cake pan.
4. Bake 50 minutes, until center is set. Remove from oven and let stand in pan 5 minutes. Invert frittata onto a large plate, then invert again right side up onto a large serving plate.