Preheat the oven to 375 F.
Defrost the spinach and squeeze out excess moisture using a potato ricer or cheese cloth.
Peel the butternut squash. Using the solid end, make butternut squash 'noodles' by using the Vegetable Sheet Cutter Attachment according to manufacturer instructions. Alternatively, use a mandoline to slice the butternut squash into thin circles.The remainder of the squash can be chopped and roasted, and added to the lasagna layers, or saved for another purpose. Mix one half of the vegan mozzarella cheese with the vegan ricotta cheese.
Stir 2 tablespoons Italian seasoning, 1 tsp salt and 1 tsp pepper into the ricotta mixture.
Ladle 1/2 cup marinara into the lasagna pan and spread to cover the bottom.
Add a layer of butternut squash noodles to completely cover the sauce.
Add 1/3 of the vegan ricotta mixture, 1/3 of the spinach and 1/3 of the remaining marinara sauce.
Repeat the layers of butternut squash noodles, vegan ricotta mixture, spinach and marinara two more times.
Sprinkle remaining mozzarella cheese on top.
Cover tightly with aluminum foil and bake for 30 to 35 minutes.
Remove foil, and bake an additional 20 minutes.
Allow to rest for 10 minutes before slicing.