With the rack in the middle position, preheat the oven to 400°F (200°C).
In a pot of salted boiling water, cook the potatoes until tender. Drain.
In a large non-stick skillet over high heat, lightly brown the garlic in 1 tbsp (15 ml) of the oil. Add the zucchini and onions. Cook for 3 minutes or until tender. Season with salt and pepper. Set aside in a bowl.
In the same skillet over high heat, brown the potatoes in the remaining oil. Add oil, if needed. Stir in two-thirds of the vegetables.
In a bowl, beat the eggs. Season with salt and pepper. Pour the eggs into the skillet and top with the remaining vegetables. Continue cooking over medium heat for 2 minutes or until the edges begin to set.
Transfer to the oven and bake for 15 minutes or until the omelette is just set.