Preheat the oven to 200˚C.
Heat the oil in a medium pan and fry the mushrooms for 5-10 minutes. Add the baby spinach and fry until wilted. Season with salt and black pepper. Set aside.
In a medium size saucepan, bring the water and milk to the boil.
Add the packet contents and stir continuously until boiling.
Reduce the heat and simmer uncovered for 8-10 minutes, stirring occasionally.
Fold the cooked mushrooms and spinach through the sauce and pour it into a 1,25L capacity oven proof dish.
Brush the filo sheets with the melted butter and scrunch each one up lightly with your hands. Top the pasta in the dish with the scrunched-up pastry and bake in the oven for 20minutes until golden and crisp.