Preheat the oven to 190°C/170°C fan/gas 5.
Heat the oil in a 20cm non-stick ovenproof frying pan over a low heat, add the potatoes and fry very gently for 8–10 minutes, turning them once, until golden and tender.
Add the leek to the pan and fry for 5 minutes until tender, then add the peas and spinach and allow the peas to defrost and the spinach to wilt for 2–3 minutes.
Whisk the eggs with the za’atar and salt and pepper. Add to the pan, mix, then cook over a low heat for 2–3 minutes, agitating the egg with a spatula until it starts to set.
Transfer to the oven and cook for 8–10 minutes until fully set. Remove from the oven and serve with the rocket and coriander.
I blend the spinach with the eggs and za’atar in a bullet blender (or regular blender) before adding to the pan, for a vibrant green frittata.