Combine all ingredients in food processor and pulse until it resembles grated Parmesan cheese.
For the Cashew Ricotta:
Combine cashews, garlic, lemon juice, nutritional yeast, oregano, parsley, basil, salt, and red pepper flakes in the bowl of a food processor. Pulse until well-blended.
Add water 1 tablespoon at a time, and pulse until the processor runs smoothly and the mixture looks creamy. Taste and adjust salt as needed.
For the Stuffed Shells:
Preheat oven to 350ºF.
Pour 1 cup marinara sauce into a 9" x 13" baking pan.
Mix the ricotta, spinach, and mushrooms together. Stuff the ricotta mixture into the shells, placing each stuffed shell in the pan.
Spoon remaining sauce over the top of the shells. Sprinkle on Parmesan.
Bake at 350ºF for 25-30 minutes.
Video
Notes
Quick soak method for cashew ricotta: Cover cashews with boiling water and let sit 1 hour before proceeding.
Super quick method for cashew ricotta: Place cashews and three cups of water in a saucepan, bring to a boil, and continue boiling for 10 minutes. Drain and rinse before proceeding.