First, make the tofu ricotta. Crumble the drained and rinsed tofu into a medium bowl, then stir in the nutritional yeast, Italian seasoning, onion powder, garlic powder, lemon juice, olive oil, salt, and pepper. Mix until the seasonings are evenly distributed, and set aside until needed. (The tofu ricotta can be made a day or two in advance, then stored in the refrigerator until you need it.)

To remove excess water from the frozen spinach, squeeze handfuls of defrosted spinach over the sink, repeating until all the spinach has been squeezed mostly dry. If the spinach is in large pieces, roughly chop it before proceeding.

Lightly oil or spray a large (4 to 6 quart capacity), preferably oval-sized slow cooker insert. Pour in approximately 1 cup marinara sauce, using a spoon to coat the bottom evenly. Break 3 lasagna noodles in half, then arrange in an even layer, overlapping slightly, on top of the sauce. (If your slow cooker is especially large, use 4 noodles.) Pour on a generous amount of sauce, mostly covering the noodles, then top with half of the prepared tofu ricotta, then half of the chopped spinach, and then 1/3 of the vegan mozzarella. Spoon on the remainder of sauce from your first jar. Repeat this layering process once more. Finish by adding a third layer of lasagna noodles, a generous amount of sauce, and the remainder of the mozzarella. Rinse out one of the jars of sauce with ½ cup water, and pour this around the edges of the lasagna: this will keep the edges of the lasagna soft during cooking.

Cook then lasagna on low heat for 6 to 8 hours, until the noodles are cooked through and the cheese is melted. Garnish with fresh basil if desired, and serve.