Preheat the oven to 200ºC/400ºF/gas 6. In a bowl, cover the fish with boiling kettle water. Put aside to soak while you trim and roughly chop the spring onions, placing them into a 30cm non-stick ovenproof frying pan on a high heat with 1 tablespoon of olive oil. Stir and fry for 2 minutes, then pile the spinach on top, let it wilt down and turn the heat off.
Spoon 100ml of the soaking water over the spinach, then drain the fish, break up the pieces and sit them evenly around the pan. Finely grate over most of the cheese and season well with black pepper. Quickly layer the filo on top, tucking it around the fish and up the sides of the pan, tearing the last sheet on top in a nutty fashion. Grate over the last bit of cheese, drizzle with ½ a tablespoon of olive oil, and bake for 15 to 17 minutes, or until golden and crisp. Easy as pie!