Add the remaining 1 tablespoon oil to the skillet and in it cook the onion and the bell pepper with salt and pepper to taste over moderate heat, stirring, until the vegetables are softened
Add the garlic and the thyme and cook the mixture, stirring, for 1 minute
Stir in the zucchini, pour in the egg mixture, and arrange the zucchini blossoms decoratively on the surface
Preheat the broiler
Cook the frittata over moderate heat, without stirring, for 12 to 15 minutes, or until the edge is set but the center is still soft, and sprinkle the remaining 1/2 cup Parmesan over the top
(If the skillet handle is plastic, wrap it in a double thickness of foil
) Broil the frittata under the broiler about 4 inches from the heat for 2 to 3 minutes, or until the cheese is bubbling and golden
Let the frittata cool in the skillet for 5 minutes, run a thin knife around the edge, and slide the frittata onto a serving plate
Cut the frittata into wedges and serve it warm or at room temperature