Preheat the oven to 400 F.
Thinly slice the potatoes. Line the bottom of the baking dish with one layer of the potatoes.
Wash and cut the cauliflower into thin slices. Layer the cauliflower on top of the potatoes.
Layer the fresh spinach on top of the cauliflower. Then add an additional layer of potato slices and cauliflower on top for a total of 5 layers.
Prepare the Vegan Alfredo Sauce: Sauté the onions in a frying pan over medium heat with vegetable stock until soft. Bring water to a boil in a small pot. Add the cashews and simmer for 10 minutes. Drain the cashews from the water.
Bring a small pot of water to a boil. Add the cashews and simmer for 10 minutes. Drain the water from the cashews.
Combine almond milk, sauteed onions, boiled cashews, garlic, nutritional yeast, lemon juice, salt, and pepper in a blender. Blend until smooth, about 45 seconds to 1 minute. Pour sauce over the vegetables.
In a food processor combine the breadcrumbs, walnuts, hemp seeds (optional), and Italian seasoning. Pulse until combined Sprinkle on top of the casserole.
Cover the casserole with aluminum foil. Bake for 50-55 minutes in the preheated oven.
Remove the aluminum foil and broil for 2 minutes to brown the top. Serve hot! Enjoy!