Preheat oven to 350 F. Bring a small pot of water to boil. Add cashews. Boil for 5 minutes. Drain, and set aside.
Bring a large pot of water to boil. Salt the water to taste. Add jumbo shells, and cook until al dente. Drain, rinse, and set aside.
While shells are cooking, add the drained cashews to a food processor. Add fresh water, apple cider vinegar, nutritional yeast, garlic, onion powder, salt and pepper. Pulse until smooth, scraping the sides as needed. Squeeze the water out of the thawed frozen spinach. Add the spinach to the food processor and pulse a few times until combined.
In a medium saucepan heat the crushed tomatoes on medium-low heat. Whisk in the Italian seasoning, salt and pepper.
Add half of the tomato sauce to the bottom of a 9x13 baking dish. Stuff the shells with about 2 tablespoon of ricotta filling. Place the shells in the baking dish on top of the marinara. Repeat until shells are stuffed. You should be able to fit about 16 stuffed shells in the baking dish.
Top the shells with the remaining marinara sauce. Bake for 20-25 minutes. Allow to cool slightly before serving. Enjoy!