Soak the sunflower seeds in a bowl of hot water for 30 minutes, then drain well.

Combine the soaked seeds, fresh water, lemon juice, nutritional yeast, garlic, salt, and olive oil in a blender. Blend for 2 to 3 minutes, scraping down the sides, until the mixture looks like thick ricotta with a little texture left. Set aside.

Heat 1 tbsp olive oil in a 10-inch / 26 cm saucepan over medium heat. Add the onion and cook for 4 to 5 minutes until soft.

Stir in the garlic and cook 30 seconds until fragrant. Add the crushed tomatoes, oregano, basil, salt, pepper, and sugar. Simmer uncovered for 10 minutes, stirring occasionally, until slightly thickened.

Heat the oven to 190°C / 375°F. If using regular noodles instead of no-boil, cook them according to package directions until al dente, then drain.

Spread about 1/2 cup of the tomato sauce across the bottom of a 9x13-inch / 23x33 cm baking dish.

Layer 3 noodles over the sauce, then a third of the sunflower ricotta, a third of the spinach, and a third of the remaining sauce. Repeat twice more, ending with sauce on top.

Sprinkle vegan mozzarella over the top layer if using. Cover the dish tightly with foil.

Bake covered for 30 minutes. Uncover and bake 15 more minutes, until the sauce bubbles at the edges and the top turns golden.

Let the lasagna rest for 10 to 15 minutes before slicing. This keeps the layers from sliding apart when you cut into it.