Preheat oven to 350 degrees.
In a large skillet, sauté onions and garlic in the olive oil until onions are soft. Add in spinach and salt, stirring well. Cook until spinach is just heated through. Add in tofu crumbles and stir well. Remove from heat and allow to cool completely.
In a small saucepan over low heat, melt cashew butter and then stir in soy milk, miso, soy sauce, lemon juice, nutritional yeast, and onion powder. Whisk until smooth and creamy.
Lightly grease the lasagna pan. Place a thin layer of the cashew nut sauce and then a layer of cooked noodles, then a layer of spinach mixture and then a layer of more sauce, then a layers of noodles, continuing until all the ingredients have been layered in. The top layer should be the spinach mixture and then sauce.
Bake in oven for 40 minutes. Allow to cool for 10 minutes before serving to allow lasagna to set.