Soak the cashews in a bowl of water at room temperature for at least 4 hours to overnight, and then drain them.
Combine the cashews and 3/4 cup water in a blender. Puree until creamy and smooth.
Heat the olive oil in a large skillet over medium heat. Sauté the onions until they start to soften and turn translucent, about 5-7 minutes.
Stir in the garlic, tomato paste, oregano, red pepper flakes, salt and pepper and continue cooking for 1-2 minutes until very fragrant.
Fold in the tomatoes followed by the spinach. Simmer for 10 minutes until slightly thickened. Remove the sauce from the heat.
Transfer the tomato sauce to the cashew cream in the blender. Puree until smooth.
Cook the pasta until al dente according to package instructions. Stir in desired amount of sauce and reheating in the skillet as needed. (If you need to thin out the sauce, you can add a splash of the starchy pasta cooking water.)
Top with chopped parsley and nutritional yeast before serving.