Mix the eggs with a fork (don't whisk it)!
Peel then thinly slice the onion.
Remove the skin of the chorizo and coarsely dice it.
Put the onion and chorizo in a hot frying pan and cook at low temperature until the sausage releases its fat content and the onion gets soft.
Meanwhile, coarsely dice the zucchini and potatoes.
Add the zucchini and potato pieces to the pan, fry for 1-2 minutes.
Pour in the egg mixture and spread it around evenly by tilting the pan.
Cover with a lid, and cook at low temperature until the egg is solid in the middle (this can be speeded up under the grill for the last 2-3 minutes).
Grind some pepper on top and serve warm. Or let it cool and cut it up into wedges/cubes for later.