Preheat oven to 325°F (160°C).
In non-stick skillet, heat oil over medium heat. Add onion and garlic; cook until onion is tender. Add zucchini; cook, stirring, for 5 minutes.
In bowl, combine cheese, parsley, eggs, spinach, salt, pepper and nutmeg; stir in zucchini mixture.
Spoon into lightly greased 9-inch (23 cm) pie plate.
Bake in preheated 325°F (160°C) oven until set but still moist in centre, 35 to 45 minutes. Serve hot or cold.
Frittata can also be cut into small squares and served warm or cold as hors d’oeuvres.