Heat the oil in a large frying pan. Add the leeks and a pinch of salt, then cook until soft. Add the garlic, coriander, fennel and chilli flakes. Once the seeds begin to crackle, tip in the spinach and turn down the heat. Stir everything together until the spinach has wilted and reduced, then scrape it over to one side of the pan. Pour a little oil into the pan, then crack in the eggs and fry until cooked to your liking.
Stir the yogurt through the spinach mix and season. Pile onto two plates, top with the fried egg, squeeze over a little lemon and season with black pepper and chilli flakes to serve.