Ingredients for two:
salt and pepper
Heat 4 spoon of olive oil, dice all vegetables and poach the onion being careful not to let it get brown.
Add the potatoes and then the courgette, salt and pepper, and let it poach on low flame until you see it done.
In the meanwhile whisk eggs, parmesan and salt and pepper and then put the vegetable from the pan to the bowl with the eggs and mix well. Pour it in the same pan you poached the vegetable (which you left heating on the flame) and leave for 5 minutes, moving the pan once in a while to avoid the egg to stick on it.
Put a flat plate on top of pan, a hand on the plate, and faster as you can turn it upside down (practice before, with empty pan, to avoid spilling the hot content).
Then gently push (with a wooden spoon, if needed) the tortilla back to the pan, to cook the other side. Usually in this moment you can find loose pieces on the uncooked side, just push them under the tortilla, they will soon stick to the rest.
Let it cool for a while and then cut in pieces!