Wash and slice the zucchini, peel and slice the onion, chop the basil and grate the cheese.
Preheat your oven to 180 °C (ca. 356 °F)
Heat olive oil in a 24 cm diameter pan suitable for oven use. Cook the onion over medium heat until lightly golden and soft.
Add zucchini with water and a pinch of salt to the pan. Cover and cook until just tender and lightly browned, approximately 8 to 10 minutes. If there is a lot of liquid from the zucchini, remove most of it with a spoon at this step.
In a bowl, whisk together eggs, cheese, basil, salt, and pepper to taste.
Pour the egg mixture over the sautéed zucchini. Cook over medium heat for 4–5 minutes until the edges begin to set.
Transfer the pan to the preheated oven and bake for 3–4 minutes, until set with a lightly golden top.
Allow to cool slightly before slicing.