Using a nut milk bag or paper towel, lightly strain the cauliflower to draw out some (but not all) of the excess water.

Add the cauliflower to a food processor and blend with 1 tbsp of olive oil, apple cider vinegar, salt, garlic powder, onion powder, and nutritional yeast. Blend until smooth and set aside. Alternatively, you can mash with a potato masher for less clean-up.

Using a small saute pan, heat 1 tbsp of olive oil on low heat. Add the spinach and allow to wilt over 1-2 minutes. Remove from the heat.

Stir the spinach into the cauliflower mixture and set aside, allowing it to cool.

While the cauliflower cools, bring a large pot of water to a boil and generously salt. Add the manicotti shells and cook for 4-5 minutes or until lightly tender. Carefully transfer the cooked shells to a bowl filled with cool water to stop the cooking process. Strain after a few minutes and transfer to a plate.

Preheat the oven to 350 F and lightly grease a 9x13" casserole dish. Add 1 cup of marinara sauce to the bottom of the baking dish.

Add the cooled cauliflower mixture to a large ziplock bag or piping bag. Cut the tip. Insert the tip into one of the manicotti shells and squeeze to fill the shell. Add the filled shell to the baking dish. Repeat with all of the shells.

Spoon the remainder of the marinara sauce over the shells and cover the baking dish.

Bake in the preheated oven for 45 minutes covered. Remove the cover and bake for another 5-10 minutes or until cooked though (adding dairy-free cheese on top if you'd like).

Serve topped with fresh chopped herbs.