Roughly chop your cauliflower into smaller pieces and add to a steam basket. Steam for about 15 minutes or until tender.
While your cauliflower is steaming, add the rest of your vegan ricotta ingredients to a high speed blender. Once cauliflower is steamed add to your blender. Pulse until you get a cauliflower mash. You still want it to be slightly chunky as dairy ricotta typically has that texture. Do not blend until smooth.
Add your pasta shells to boiling water and cook according to the instructions on the box.
Add the spinach to your steam basket along with salt and steam for about 1 minute or until wilted.
In your baking pan spread about 1/3 of your tomato sauce on the bottom of the pan. Stuff your cooked pasta shells with some spinach and about 1 tbsp of cauliflower ricotta. Lay them flat in a single layer in your pan. You do not want more than one layer. Once all your shells are laid in the pan, pour the rest of your tomato sauce over the top of them.