In a medium bowl, whisk together the eggs, Parmesan cheese, salt, pepper and chives;
In a 10-inch ovenproof non-stick skillet, heat 1 tablespoon of oil over medium heat.
Cook half the zucchini slices until tender, about 3 minutes, then move them to a small bowl.
Repeat with the rest of the zucchini and reserve.
Add the remaining tablespoon of oil to the skillet and cook the onions, tomato and garlic for 3-4 minutes, or until the onions are tender. Return the zucchini to the skillet, evenly distributing it.
Add the egg mixture, and cook for 3 minutes, or until the bottom of the frittata is just set.
Place the frittata in the oven and bake for 12 to 15 minutes, or until it is completely set and golden brown. Carefully cut into slices and serve.