Sauté the green onions (scallions) and leeks in a pan with a splash of olive oil until soft. Add the spinach and herbs and cook for a bit longer. Transfer to a large bowl and set aside to cool slightly.
Brush your pie dish with the melted butter then start layering the filo pastry, brushing each leaf with butter, in the dish letting the ends hang over the edge.
Score the pastry before baking to make it easier to slice. Sprinkle with sesame seeds and bake for 45 minutes, covering with foil after 15-20 minutes to avoid the pie colouring too quickly.