Place a frying pan on the heat and add a drizzle of oil. Slice the mushrooms and tomatoes, and throw them into the pan. Let them cook for about 8 minutes, stirring occasionally before adding the spinach. Cook for a further 2 minutes before switching off the heat. Take everything out of the pan and set aside for later.

Grab a mixing bowl, crack the eggs and beat them together to form a smooth mixture. Tip in the cooked ingredients and season with some salt and pepper.

Heat up your frying pan again and pour in the frittata mixture. Use a wooden spoon to distribute the fillings evenly across the surface of the pan. Let it cook for about 10 minutes - and no stirring! You're looking for the eggy mixture to start to set around the edges. 

At this stage, flip the frittata over and cook the other side in the pan (we recommend putting a plate on top and turning it over). Alternatively you could put it under the grill for a couple of minutes. Serve the frittata with ketchup or hot sauce drizzled on top.