Soak the cashews: Cover raw cashews with hot water and soak for 20–30 minutes (or overnight in cool water). Drain before blending.
Cook the pasta: Boil the ziti in generously salted water until just shy of al dente (1–2 minutes less than the package). Drain and set aside.
Sauté aromatics: In a large skillet, warm olive oil over medium heat.
Add the onion and a pinch of salt. Cook 5–7 minutes until soft and translucent. Stir in minced garlic for 1 minute.
Make the sauce base: Pour in marinara or crushed tomatoes.
Add Italian seasoning, red pepper flakes if using, and black pepper. Simmer 5–10 minutes to thicken slightly. Taste and adjust salt.
Blend the cashew cream: In a blender, combine soaked cashews, water or plant milk, nutritional yeast, lemon juice, 1/2 teaspoon salt, and a crack of pepper.
Blend until completely smooth and creamy. Adjust thickness with a splash more liquid if needed.
Combine sauce and cream: Stir about two-thirds of the cashew cream into the tomato sauce until it’s rosy and velvety. Reserve the rest for dolloping on top.
Add greens (optional): If using spinach, stir it into the warm sauce until just wilted.
Toss with pasta: Add cooked ziti to the creamy tomato sauce and fold gently to coat.
Assemble: Transfer half the pasta to a greased 9x13-inch baking dish.
Sprinkle with half the vegan cheese (if using). Add the remaining pasta and spoon the reserved cashew cream in swirls on top. Finish with remaining vegan cheese.
Bake: Cover with foil and bake at 375°F (190°C) for 15 minutes.
Uncover and bake another 10–15 minutes until bubbly and lightly browned at the edges.
Finish and serve: Let rest 10 minutes so it sets up. Top with chopped basil or parsley. Serve warm.