Preheat oven to 350. Line rimmed baking tray with unbleached parchment paper.

Clean mushrooms with damp paper towel. Remove stems, mince and set aside to include in filling.

Place mushroom caps upside down (so removed stem is face up) on prepared baking tray. Brush with 1 Tablespoon olive oil, or use an olive oil spray. Bake for 10 minutes to soften.

MAKE THE "CHEESE": Use a coffee or spice grinder, small food processor (or a sharp knife and some elbow grease) to combine nuts, oregano, onion powder, garlic powder, salt and optional nutritional yeast. Pulse until crumbly and resembling parmesan cheese. Set aside.

MAKE THE FILLING: In a heavy skillet over medium heat, swirl in remaining 1 Tablespoon oil, add in the reserved minced mushroom stems and diced onions. Cook, stirring often for about 3 minutes while stems release their juices. Sprinkle with S+P, grate garlic over pan and continue to cook, stirring for 2 more minutes while onions continue to soften. Stir in cauli-rice until well incorporated. Turn off heat. Mix in all but 1 Tablespoons (set aside for topping) of nut mixture, and the spinach/parsley.

Scoop filing into the par-baked mushrooms. It's Ok to overstuff. Sprinkle with the nut mixture you set aside and bake for 15-20 minutes, until mushrooms are tender and topping is golden.