Preheat oven to 390°F (200°C)
In a large bowl mix together the cassava flour and salt. Then add the olive oil and water and mix until you get a dough.
Roll out the dough between 2 parchment papers, using a rolling pin. Remove the top parchment paper and transfer the dough to a 24 cm / 9.44 inches diameter pie tin on the other parchment paper.
Prick the pie with a fork to prevent it from inflating. Put it for 10 minutes in the oven to precook it.
In the meantime, peel and dice the onion. Heat a little bit of oil in a skillet and transfer the diced onion to the pan (if you choose to add bacon cubes to your pie, cook them along with the onion, without adding any oil). Clean the mushrooms, slice them and add them to the pan along the spinach. Let the whole thing cook on medium high heat until the spinach reduce by half.
Put the pumpkin (or butternut) in a large bowl and puree with a fork. Add all sauted vegetables to the bowl, season with salt and mix all the ingredients together. If you can have goat or sheep cheese, add some cheese cubes to the mix.
Pour the mixture onto the crust and bake for about 25 minutes or until cooked through. To add a little glow to the pie once cooked, lightly brush or spray a little bit of olive oil. And voilà! Serve immediately!Bon appétit !