Break the eggs into a large bowl and whisk together with a fork. Cut the ham into small pieces and finely chop the parsley (if using) and add both to the eggs. Trim the spring onions and courgettes and finely chop. Heat the oil in a large frying pan and fry the onion and courgettes for about 5 mins until soft and pale golden.
Pour the egg mixture into the pan with the vegetables, turn down the heat and quickly stir to move the eggs around the pan to mix everything together. Then lower the heat still further and cook the frittata, uncovered, for about 4 mins or until there is only a little runny egg left on the top.
Preheat the grill to medium, sprinkle the grated cheese over the top of the frittata and brown under the grill for a few more minutes until the top is golden and bubbling and the egg is fully cooked. Cut into triangles and serve.
Cook's tip: for baby, purée a little of the cooked courgette and spring onion mixture with 2 tbsp of cooked frozen peas and mix with a little mashed potato.