Preheat the oven to 400°F (204°C).
Sauté the chopped onion in a little olive oil in a non-stick frying pan until glossy, about 5 minutes.
Add the two chopped garlic cloves and cook for 1–2 minutes until fragrant.
Stir in the chopped tomatoes, tomato puree, paprika, oregano, basil, salt, and pepper and simmer for about 5 minutes to make the marinara.
Meanwhile, make the cashew white sauce: blend soaked cashews, 1/2 cup dairy-free milk, 1 garlic clove, nutritional yeast, nutmeg (if using), salt, and pepper until smooth and creamy.
Press the firm tofu to remove excess water, then crumble it into a mixing bowl with your fingers.
Add the cashew white sauce to the crumbled tofu and mix until evenly combined.
Fine-chop or pulse the fresh spinach in a food processor, squeeze out excess moisture, then fold the chopped spinach into the tofu-cashew mixture.
Spoon a thin layer of marinara into the bottom of the oven-safe dish.
Assemble the lasagna with 3 layers: pasta sheet, marinara, and the spinach-tofu ricotta, repeating until you have used three stacks (this fills a 9×7×2-inch dish).
Finish with a top layer of marinara and sprinkle the dairy-free grated cheese or vegan Parmesan (or extra nutritional yeast) over the surface.
Bake in the preheated oven for 30 minutes, then remove and let rest a few minutes before serving.
