Cook off the onion until soft in olive oil, so mins.
Beat eggs, ¾ of the cheese, spring onion & herbs together.
Add diced cooked potatoes.
Add cooked onions, including the oil from the pan you cooked them in.
Wipe out pan, splash more oil, add frittata mix to very hot pan, turn down heat, arrange your courgettes however you wish, add remaining cheese.
Grill under hot grill for around 15 mins, until egg is cooked & frittata nicely coloured.
