Heat olive oil in a large nonstick pan over medium-high heat. Add the onion, garlic, and tomato paste and cook for 5 minutes until onions are softened and fragrant. Add the crushed tomatoes, dried oregano, and salt, and cook for a further 3–4 minutes, stirring frequently.
Add the extra firm tofu, nutritional yeast, apple cider vinegar, tahini, and almond milk to a blender or food processor.
Blend on a low speed for a few seconds until well combined.
Transfer the tofu ricotta to a frying pan over medium heat and add the spinach leaves. Sauté for 1–2 minutes or until the spinach wilts, and season to taste with salt and pepper.
Spread a thin layer of tomato sauce in the bottom of a 9x13 baking dish. Arrange a single layer of lasagna noodles on the bottom of the pan. Spread ½ of the tofu ricotta and spinach mixture evenly on top of the noodles. Add a few spoonfuls of tomato sauce and spread evenly across the filling. Top with another layer of lasagna noodles.
Repeat with another layer of ricotta-spinach mixture, sauce, and noodles. Spread a thick layer of tomato sauce over the top of the lasagna. (You may have some extra sauce leftover.)
Bake for 50–60 minutes.
If desired, you can melt some vegan mozzarella on top of the lasagna or sprinkle with vegan parmesan for serving.