Preheat the oven to 400F and line a baking sheet with parchment.
To a food processor, add all the crust ingredients and pulse till a parmesan cheese-like texture begins to form. Remove the crust and set aside.
To the same processor, add the 1/2 walnuts and pulse till a ground-like texture develops (around 15 seconds), remove from the processor into a small bowl, and set aside.
In a medium pot, add 1 tbsp. olive oil and gently cook your onions and garlic on medium heat for 5 minutes. Stirring frequently to prevent burning.
To the pot, add all your seasoning and spices. Stir till all the onions and garlic are coated with the seasonings/spices. Cook for 2 minutes before adding the olives.
To the pot, add the spinach and cook down till completed wilted and there is no moisture left in the pot.
While that cooks, remove the stems from the mushrooms/use a spoon to gently remove from of the mushroom center to create a concavity to stuff them mushrooms in. Refer to the video below for more direction.
Place the whole portobello mushrooms onto the baking sheet and cook for 10 minutes in the oven.
Chop up the stem/center of the mushroom finely and place into the pot with the spinach. Brown the mushroom well and cook for at least 5 minutes.
To the pot, add the 1 cup of processed walnuts and cook for 5 minutes or till golden and toasted. Now add the fresh herbs and feta. Cook for another 5 minutes till everything is well combined. Taste for seasoning for stuffing each mushroom. If any salt is needed, add as desired.
Remove the portobello mushrooms from the oven and gently stuff each with the spinach/walnut stuffing. Top each with your desired amount of crust and cook for 20-25 minutes in the oven. See notes below for how to store your leftover crust.
Enjoy!
Video
Notes
Crust Storage: Store any excess crust in a tightly sealed jar, in the fridge, for up to 1 week. Tip: can be used as salad toppings, in "meatballs" etc.Servings: This recipe serves 3 as a main but if depending on the size of your portobello you may be able to make up to 5. Note: we used large portobello mushrooms.Oil: If you prefer to make this recipe oil-free, then simply use water or vegetable stock to cook/steam the ingredients like the onions/garlic and walnuts. I recommend 3-4 tbsp. water or stock to replace the 1 tbsp. olive oil.Seasonings/Spices: This recipe is quite versatile, so if you prefer or fancy other herbs/spices then we encourage you to have fun and play around with those ingredients.Feta: Vegan feta is completely optional. If you prefer or aren't vegan, regular feta is fine!