Preheat the griller to high. Rinse and dry the spinach and put aside; chop enough parsley to give about 2 tablespoons and put aside.
Heat the oil in a large frying pan. Halve, peel and finely chop the onion. Fry the onion over moderate heat for 3–4 minutes, stirring, until soft but not browned.
Clean and quarter the button mushrooms, add to the chopped onion and fry, stirring frequently, for a further 3–4 minutes.
Add the spinach and cook over fairly high heat, stirring frequently, for 3–4 minutes, until the leaves have wilted and the excess liquid has evaporated. Stir in the cashews and reduce the heat to low.
Break the eggs into a bowl, then add 2 tablespoons cold water and the chopped parsley. Add salt and pepper and beat together.
Pour the egg mixture into the spinach and cook for 5 minutes, until the egg is set and golden.
Grate the cheese and sprinkle over the top. Place under the griller and grill for 2–3 minutes, until the fritatta is set and the top is golden. Alternatively, place the frittata on a baking tray under the griller.
Serve the frittata, hot or cold, with crusty bread and a tomato salad.
This was very nice. I added turkey bacon because I like meat in my frittatas. This really had a lot of vegetables.. a little too much really. I am usually one who adds more veggies, but this time I would decrease them or add more eggs. All I could taste was mushrooms. The nuts got lost for me, so I would instead sprinkle them on top.. they would stay crunchier that way and not get quite so soft - 06 May 2013