Preheat the oven to 375 degrees F.
Heat the oil in a large dutch oven over medium-low heat. Add the onions and cook for about 5 minutes until they begin to turn translucent. Add the garlic, oregano and red pepper flakes and cook for 1 minute, being careful not to burn the garlic.
Carefully add the vodka, standing back to avoid flames, and simmer for 5–7 minutes, until the mixture is reduced by half.
Add the tomatoes, 1 teaspoon of salt and 1/2 teaspoon of black pepper. Cover the pot with a tight-fitting lid and place it in the oven to bake for 1 1/2 hours.
Meanwhile, bring a large pot of heavily salted water to a boil. Add the pasta and cook according to package directions, until al dente. Drain, reserving about a cup of pasta water, and set aside.
Pour the tomato mixture, cashews and water into a high-speed blender and blend until completely smooth and creamy. Be sure to vent the top with a towel to let the pressure out—the mixture will be very hot. Return the blended mixture to the dutch oven.
Add the fresh oregano, 1 teaspoon of salt, and 1/2 teaspoon of pepper and simmer, partially covered, for 10 minutes. Add the pasta to the sauce and cook for 2 minutes so that everything comes together nicely. Add a bit of reserved pasta water if you like a thinner sauce.
Off heat, stir in 1/2 cup of the vegan parmesan cheese (if using) and serve sprinkled with extra herbs and parmesan.