Preheat the oven to 220 degrees Celsius.
Preheat a nonstick pan over medium heat with some olive oil.
When the pan is hot add the yellow onion and garlic and fry for 2-3 minutes, until it starts to get soft and golden brown.
Next add the mushrooms and spinach and fry until soft and tender.
Add the creme fraich, white wine (if using), vegetable stock cube, lemon juice, cumin, paprika powder and mix until combined. Taste and season with sea salt and black pepper if needed. Let it shimmer until the sauce has thickened.
Meanwhile slice the zucchini using a mandolin into thin stripes (I used thickness 3 out of 4).
Take oven safe baking pan and add zucchini slices at the bottom of the pan. Depending on if your doing three of four layers add either one third or one forth of the filling on the zucchini stripes. Add a little crumbled feta cheese on top.
Cover with new zucchini stripes and repeat this procedure until you have used all the mushroom/spinach filling.
Add zucchini stripes on top and then the grated cheese.
Bake in the oven for approximately 25-30 minutes. Then turn on the broiler and bake for another 2-3 minutes, until golden brown.