Add olive oil to the fry pan you cooked the mushrooms in (on medium heat). Don't wash it in between because the slight mushroom flavours with the spinach is pretty yummy.
When the oil is hot, add the spinach. Turn in pad when it starts to wilt - this will only take a few seconds. Remove from pan as soon as it starts to wilt and loose shape. You still want it to have the vibrant green colour and you definitely don't want to singe it.
Recipe by my vegan plate at https://www.myveganplate.com/big-breakfast/