Add the cashews to a bowl or glass jar and cover with a few inches of cold water. Cover the jar and soak the cashews in the refrigerator for at least 8-10 hours.
Drain the cashews and rinse them well. Add them to a high speed blender along with the nutritional yeast, lemon juice, salt, and water. Blend for 1-2 minutes until completely smooth.
Heat the olive oil in a large dutch oven or high-walled skillet over medium high heat. Add the mushrooms and onion and saute until tender, about 7-8 minutes.
Add the garlic, dried plums, and thyme. Cook until the garlic is fragrant, about 1-2 minutes.
Add the cauliflower and stir well to combine. Cover and cook, stirring occasionally, until the cauliflower is tender, about ten minutes
Remove the lid and pour in the cashew cream. Cook for a few more minutes, stirring constantly, until heated through.
Stir in the spinach, parsley, and lemon zest and remove the pot from heat. Season with salt and pepper to taste.