First, drain the packages of tofu and place in a large bowl. Let sit for 5 to 10 minutes while you prepare and gather the other ingredients. Some water will drain out of the tofu as it sits. Discard the water, then add the remaining ricotta ingredients to the bowl. Mash with a fork until the ricotta is fluffy and fully incorporated.

Preheat a large saute pan over medium heat. Dry sauté the onion and mushrooms until softened and dry, about 8 minutes. Add chopped spinach and tamari, if using, and cook for another minute or until wilted. Set aside.

Lightly oil the bottom and sides of a 6-quart slow cooker, and turn it on to HIGH so it can heat while you assemble the lasagna.

Spread a thin layer (about 1½ cups) of marinara in the bottom of the crockpot, followed by 3 pasta sheets, broken to fit (doesn't need to be perfect). Spread with one-third of the ricotta (about 1½ cups), followed by half of the sautéed veggies, and approximately ¾ cup shredded vegan cheese.

Repeat the layering process as written above. Then, for the 3rd and final round, skip the veggies and shredded cheese and finish with sauce on top. So the 3rd round looks like this: sauce, pasta, ricotta, sauce.

Cover the slow cooker and cook on high for 2 hours.

After 2 hours, carefully lift the lid straight up to avoid dumping condensation onto the lasagna. Sprinkle the lasagna with more shredded cheese, cover, and cook for another 30 minutes.

The cheese should be melted and the lasagna should be lightly bubbling. Turn off the crockpot and let the lasagna stand for anywhere from 30 minutes to an hour (with the lid askew). The lasagna can be served right away, but it will be fairly messy, more like a casserole. The rest time allows the lasagna to cool slightly which helps it set. Serve with a side salad and enjoy!