Press the tofu for at least 15–20 minutes to remove excess moisture.
Crumble the tofu into a bowl. Add lemon juice, nutritional yeast, garlic, Italian seasoning, and salt. Mix well to form tofu ricotta.
Cook lasagna noodles according to package instructions if needed. Drain completely.
Preheat oven to 375°F (190°C).
Spread a layer of marinara sauce on the bottom of a baking dish.
Add a layer of noodles, then spread tofu ricotta evenly.
Add spinach and more sauce.
Repeat layers until ingredients are used.
Top with vegan mozzarella if using.
Cover with foil and bake for 30 minutes.
Remove foil and bake another 10–15 minutes until heated through.
Let the lasagna rest for 10–15 minutes before slicing and serving.