Heat large pan over medium heat and add 2 tbsp of water. Add 1 of the diced onions and 4 cloves of garlic. Cook until soft, adding a tbsp or 2 of water as needed to prevent sticking.
Next, add the mushrooms and cook until browned, working in batches if needed. Add the carrots and zucchini and cook for a few more minutes. Finally, add the thawed spinach along with salt and pepper to taste.
Preheat oven to 400 degrees Fahrenheit and set vegetable mixture to the side.
Begin making Bechamel Sauce. Add cauliflower florets to large pot of water, bring to a boil and cook for about 10 minutes, until florets are soft.
Once cauliflower is soft, drain and add to blender. Blend until smooth, adding non-dairy milk if needed to reach desired consistency. Set aside while making the rest of this sauce.
Put the other onion in a large saucepan and heat over medium high heat until translucent. Add 1-2 tablespoons of water as needed to prevent onion from sticking.
Add the rest of the garlic, thyme, and basil and cook for another minute.
Add 1/4 cup of nutritional yeast, nutmeg, salt and pepper to taste and cook for another couple of minutes.
Add the onion and garlic mixture to the cauliflower puree along with Braggs Liquid Aminos and lemon juice and blend until smooth. Add the remaining nutritional yeast, adding 1/4 cup at a time until desired taste and consistency is reached.
Now, it is time to assemble the lasagna.
In a large baking pan (11x7x2) place a layer of marinara, followed by a layer of bechamel sauce, followed by a layer of noodles. Then add another layer of marinara, half your veggies, followed by another layer of bechamel and another layer of noodles. Continue with more layers. Finish the top with a layer of marinara and bechamel sauce.
Cover with tin foil and bake for 30 minutes. Then, uncover and bake for another 10 minutes or until the top begins to brown in places. Remove from oven and allow to cool for at least 30 minutes before cutting and serving.