Set a large skillet over medium-high heat and add 30ml of olive oil. Once shimmering, add the sliced mushrooms. Cook, stirring frequently, until the mushrooms have reduced in size and are nicely golden brown - about 10-15 minutes.

Add the white parts of the green onion along with a generous pinch of salt and cook for a further 3 minutes.

Add the spinach, stir carefully to combine with the mushrooms and cover the pan for a minute or two, just to allow the spinach to wilt more easily. Remove the lid and cook the spinach, stirring constantly, until it will completely and has released all of its moisture - another 1-2 minutes.

Scrape the mushroom and spinach mixture into the pie crust and spread it evenly across the crust. Pour the egg, milk and cheese mixture over the spinach.

Transfer to the oven and bake for 30-35 minutes or until the quiche is browned on top and doesn't wobble in the centre when shaken. Remove from the oven and allow to cool for 15 minutes before slicing and serving.